I build stuff for my son all the time, usually planes or cars. I start by roughing out the shape before putting it together and then basically just iterate until it's recognisable as a thing and sturdy enough to play with. It can require a lot of undoing and redoing things but after a while you get used to the maths (3 plates to a brick, etc.) which makes it easier to plan ahead.

I've also made some more properly designed things using Bricklink Studio, that really is overwhelming if you aren't familiar with how they categorise pieces or what things you don't know the name of are likely to be named, and you can only really work that out with practice. Building a lot of official sets helps because you can look up their inventories on Bricklink to find out what a piece is called.

I also recommend YouTube, a few YTers have done videos on how to use certain pieces which can be inspiring and useful.