Great, so is there an Guide on how to train the Girls ? :/
Not a guide but what do you want to know?
The girls gain exp in different qualities based on actions they perform. You can equip them with good gear, put them on follow, and go farm the world, training them on where all the gather, dig, mine, fishing, farming, insect collection, etc., points are. You know they acknowledged the activity because they will clap/cheer. Then when you turn them loose on their own they will perform whatever actions they have been shown how to do. They can do it on their own eventually, but like my first girl, I didn't know what I was doing yet, my 4th girl got the best start, she passed all the others quickly and has by far the highest stats.
You need to get their trust, instinct, and sociality up first if you want them to advance their transformation quickly. Trust will make them listen to your commands (too well may I add, they will work until collapse etc., so you need to micromanage them a little, make them eat, and take rest breaks), instinct will make them focus harder on their tasks with fewer distractions, and sociality will enable them to both learn from and teach the other girls, advancing both a little.
You need to equip them with the appropriate skills early on to advance their growth fastest. I thought that transformation dictated growth, but others have pointed out that the growth level to add skills (on the character status card, top right box, skills: Normal/H-Scene) you need to reach 3 hearts, which requires a lot of interactions, like listening to her problems, asking her how she is/how she feels, and gift giving, as well as desireable H interactions, but nothing rushed/forced. Thereafter you will want to add skills that say "[variable action X] will increase [variable stat]." I.E. Skill Chip description states: "If the girl achieves orgasm during vaginal intercourse her instinct will increase exponentially," or "If the hero cums during female controlled H-scene, she will gain slightly more trust." To add the skills you need to go into the phone's status screen and click on the "-----" at the top right under skills: Normal/H-Scene to add skills once available.
You want to farm up colognes (mistranslated "colons" ROFL), magazines/books, and gems which are gift you can give to the girls to add +10, +50, and +100 to different parameters of their personality traits.
You will want to design multiple outfits and save them as templates in the character creator so the girls can change their clothes often, something necessary for her "Girl-power" progress to increase. Be sure you make some day clothes sets, work clothes sets, bathing attire, and pajamas for the girls.
You will want to run around and collect a large amount of resources to build up all three possible bases to have:
1. A non-leaking roof: this is simply making a solid structure without offset pieces, but it necessary that they structure doesn't let in water.
2. A bed
3. A heat source
These first three are absolutely essential to keep your girls healthy and prevent them from passing out, which will increase their darkness. Giving them privacy when doing personal things is also important, like bathing, changing, using the bathroom.
4. A cooking station
5. A dining/picnic table
4 and 5 are for optimal health of the girls
Non-essentials that will increase their stats thought time
6. A bath
7. A toilet
8. A place to change their clothes (raises Girl-Power stat)
These are for their happiness and some skill points with transformation exp:
9. "Field" farm plots with plants. Note: they will tend the plants and water plots without plants planted, but those tended will yield more items (usually 3 different ones) when harvested.
10. Pets - cat, chickens, fish, butterflies, robots, hybrid special pets made through crafting, all give the girls exp and positive feelings.
11. Fans, not as important as a heat source, but helps maintain temperature normality.
13. Books/desks with reading materials, helps girls increase their underlying intelligence which helps them advance all skills slightly faster.
14. Chairs, benches, stools, etc., enables the option of "a girl takes a break," improves endurance and prevent the faint condition "overworked."
15. Swing, Slide, TV, Video Games, etc., enables the girls to be "playful," which positively effects mood.
This final thing is another must, but is not for the girls at all...
16. Medicine table: needed to make various medicines and remedies to negative status effects.
The final things are mostly you, commit more time to running around and farming early on. Advance your tools as quick as possible to farm the three star gather points. Be sure to also expand your bag to give you more time to collect and dump off excess items in the chest frequently. Check the SHOP daily to see if she has anything important like items to boost the girl's stats, or things needed to advance your gathering capabilities. Try to take time out each day to commit to at least one girl and spend time with her. Check her status and see what she needs most. If she is hungry and has a cold, give her medicine then take her to eat. If her "naughty" is 100% then offer her to H or talk dirty to her and see if she reciprocates. If she doesn't immediately take, then just move on to another topic, if you force her she will dislike you and her darkness and vigilance will increase. Once you go beyond a certain point, she will be unable to love you again, unless you craft the stat reducing magazines from the stat increase items, one of each for one stat decrease item. So you have to trade +160 for -50.
That about covers the basics... If I think of anything I will edit below this line with a line leader "EDIT:" attached so you know it is new...
EDIT: Keep your food storage full with the best food you can provide. In the beginning this will be mostly boiled river water and fried fish, but as you farm and fish more you will be able to make better dishes and drinks. Just make sure that your food storage always has premade food available and some ingredients for the girls to make food (so they can get that girl-power and instinct bonus exp if they want).
EDIT: Proceed slowly and unlock girls one at a time. It is much easier micromanaging one girl while building your world, than 3 or 4... They will distract you from your goals often... They are almost the antagonists...
EDIT: Do not rush to H girls, as a matter of fact, early on, even when they approach you, just speed the H along and select "cum together" then exit as soon as she stops talking. Let her rattle on her babbling to the end when the "reinsert/pull out" option appears on the bottom left then exit, so she gets full exp/credit for the H. The H interaction speeds up time and if you get her off 2 or 3 times, you will have lost half the day that you could have been farming. This will also force the girls to be more social which will build their sociality and girl power, as well as make them collectively learn from one another while you attend other tasks. Just make sure you watch their hunger and fatigue in the status window.