where should i s t a r t

so first you fall into the underground and there is all of these monsters who try to fight you and then they attack you and you have choices to see there defense and everything and you can fight, act, item(healing HP) and spare. to get a certain ending (genocide route) you have to fight. that also leads to a boss fight, to get the good ending you have to keep sparing. so yeah hope that helped :P