how does the flirting system work?I don't understand a thing about it and I only have negative result...I need an explanation please.
Protocol I use is to ask if they want anything, give them the thing they're after (sci fi novel if they like science, art supplies if they like filmography, "how to win friends" book if they like politics, energy Drink if they like music, and cash if their into sports.), flirt and choose to say something insightful, then choose whichever option corresponds to the thing they asked for. Ask their hobby for more relationship points (even though we need the info here less now, since we've already given them their treat) and by now you should have two hearts in the friendship stat.
If it's a student (Don't worry, this is apparently a remedial education school; only those over 18 can enroll) I then ask about their parents, then their parents job, then about their friends. By this point you should have 3 hearts in friendship, and you can usually ask for their phone number. If it's a generic parent (or non PTA faculty I haven't hired yet) I ask for their job which may be enough to get the three hearts, and, hopefully, the phone number. If not, you can ask them if they're interested in anyone, and that should give some extra points. Once you have the phone number call them (anyone you have the number for) up on the weekends and afternoons and select social call, and then "just small talk" and eventually your "friendship bar" will fill up (at about a heart a call, and you can make multiple calls a day as long as they aren't back to back. calling a few other contacts inbetween is usually enough to go back to one you're focusing on).
When this happens you will get a heart in the relationship stat and should now probably be able to complement their personal and their body in the flirt dialogue. (body is easier, since it corresponds to the personality trait used for saying something insightful. If they like science appeal to the scholar, if they like filmography appeal to the artist, if they like politics appeal to the leader, if they like music appeal to the rogue, if they like sports appeal to the athelete) unlike saying something insightful, you can use these more than one time, and you can still get some points if their relationship is high enough and you use the wrong option.
Once you get a few hearts in relationship (how many depends on the stats, energy, arousal etc. of the individual, some people you can get into right away before you have any hearts in relationship, though unless they are clearly corrupted, it's not worth the risk to ask them early) you can start asking for sex and working your way through it starting with fondling each other, then going back to the top of the options and working from the options higher on the list to lower until you're at maximum hearts or they'll go on a date.
Edit: this all assumes you have the information set to the "lore" setting.