How hard would it be for a beginner to make something like this?

I read those already. but do I paint it on freehand or what

Unless you have access to an airbrush and really good stencils then yes you're looking at doing it freehand. Since you have no experience I highly reccomend buying a few cheap figures to practice on first. Practice until you get a good feel for what you're doing. You'll want some good brushes with fine, small tips to paint the legs (or the black lines between the legs). I myself paint the body and abdomen first, then paint the legs. I usually start with the top leg, then carefully paint each one under the other. Paint the legs until they reach the middle of the figure's side. This will help you align the legs when you paint the back. When I paint the spider on abdomen of the figure I usually protect the top with some quick drying superglue followed by a few coats of vallejo varnish to seal it. Again, practice this on some cheap figures first so you don't mess up your movie figure.

Once you've painted your spider symbols you'll want to go over it with some sealant. I usue Vallejo varnish from hobby lobby, but their are other brands you can use if that's not available in your country.

what just paint it on freehand? I really need a reliable cover all guide cause I have no experience with painting anything

I would reccomend checking out the tutorial section then. It covers pretty much any topic you need, including paint applications. I used it extensively when I first started out.
https://www.figurerealm.com/customtutorial

I can try to answer any questions the guides might not cover, but check them out first.

Alright, you need parts from two figures for this. You need movie Venom's body, and an older ML Venom head. You would need to paint over the veins and paint the symbol on the body and swap out the heads. Technically this would be a simple custom, you just need to paint the symbol, seal it, and you're done.

It's not a bad choice for a beginner. I recommend painting the symbol on some practice figures first until you're confident you can do it on the movie venom.

If you prefer you can hire someone make one for you. I'd encourage trying it out yourself first just to see what you can do.