what engine for what use?

@Giova or a lot of engines and kerolox

Really heavy rockets: Hydrolox
Medium weight rockets: Methalox
Small weight rockets: Kerolox

I can give you a very basic idea:
1.If you made a rocket that's really heavy you can use solid rocket boosters to boost your rocket,to make a solid rocket motor you can use the solid rocket motor or you can convert any other engine you want.
2.Liquid engines are one of the most important ones,using liquid engine you can change the throttle and your crafts pitch and headings,you can also change gimbal range but solid rocket motors dont have gimbal.
3.Engine cycles are really important thing,if your making your rockets core stage than should use a engine cycle that can provide enough thrust to your rocket like:(1)if your rockets is heavy than you should use full flow staged or staged or gas generator 2.(2)if you are making 2nd stage you can use gas generator 1 or staged and if you want more power in your 2nd stage you can use full flow staged it has more chamber pressure.Nozzel throat size also matters and nozzel length is also really important.increasing nozzel length can increase your rockets efficiency in vaccum and increasing throat size decrease overall efficiency but increases thrust.
4.If you want to make a satellite with engine you can use pressure fed engine cycle or electric cycle that should be enough for a small sat.
4.titan engine uses methalox and dragon engine is nuclear engine so it uses water or hydrogen and all the other use kerolox but you can change fuel types.if it feels hard to you to understand which engine uses what fuel you should play the game for a while.
I hope it may help you😁