itch.io

I'm no expert but in most cases you want to control as much of player movement as possible from script. Acceleration, deceleration, max velocity etc. there is many tutorials here is one I found just now: https://craftgames.co/unity-2d-platformer-movement/
But i believe there are better (and of course worse too) on youtube and maybe even somewhere on itch. Making movement for platformer is a hard to master thing. At first it's good to try to emulate original Mario as it has one of simplest and most intuitive movement schemes, but if you want to get a feel of how good can excellently crafted platformer movement be I recommend playing Celeste or Super Meat Boy.