You've got a few options that probably will depend on where you want to end up (personal use, business use etc).
I personally use Fusion 360 as there is a free for hobby/personal use version if you jump through the right hoops in the right order and renew it each year AFTER it has expired - you can't do it before.
OnShape is another that's all web-based and seems to be quite popular too.
Solidworks is also well thought of but I don't think there's a free version so it's probably more applicable if you're going to be usiyit professionally and the field you're looking at prefer it.
There's also things like Tinker CAD but - and I may be doing it a disservice - I think it's more aimed at STLs and tweaking stuff than a full featured package.
Irritatingly, I'm not sure you'll find SketchUp a lot of help - it's the path I started down but doesn't seem to have kept up and other things are different enough that it doesn't help a lot.
As for where to learn, YouTube is probably your most accessible. There are paid for online courses too, depends on your learning style/pace.
@Cenedd Exactly what I needed, I've got Fusion 360 installing as we speak and I'll start there much appreciated.
I've got no business use but a few projects I'm planning to do which currently don't have a solution and I'm probably not the only one thinking it.
Any recommendation on specific YT guides to take a look at?