Aliasex Not really surprised you got lost/bewildered as the translation is MTL, so here's a few things:
NPC's with the symbols above their heads are the ones whom you can trigger story progression through although the symbols stay after you trigger the progression. The places you can go to increase as you get further through the story (although three doors will be dead-ends or not open because they're for future updates that I'm further doubting will come) so best way to progress is to explore until you get a cut-scene or go into an new area you weren't able to get into or has some attempts of environmental story telling stuff in it. (e.g. new dead bodies, different placement of enemies or objects)
The H content of the game is purely your female party members and it only occurs when they've been fully captured and an enemy is interacting with them at the holding/capture point. As a result of this if they never end up reaching those points you'll never see any H content until the very end where the story forces it. There's an item you can equip that will make it so enemies will no longer see you as long as you leave them alone so you can just watch everything occur. (Although if you are weak then you'll struggle to free your entire party) If you do plan to let everyone or some of your party get captured and go through H scenes fully (to orgasm) multiple times then you'll at some point end up with them becoming `broken` (usually after 10 capture orgasms without an rest period at base I believe) and you'll need to talk to your first NPC party member and use the offering options to reset them so they'll fight effectively again otherwise they will get captured in seconds and do nothing in combat.
Doing offerings at the altars are ways you can reset boss encounters so they'll trigger again, however they do not scale so the first few are instant kills when you get to the middle of the story roughly. Only reason why you do it is if you want to grind the materials you get for cash quickly. (Which I only had to do for the last area as prior to it you're easily OP)
There is no proper in-game tutorial instead you have to guess around and find out in-game or read the Dev's website/separately included tutorial in the game's files via HTML.