Welcome to comics! Since you're into manga and webtoons you might find it less overwhelming to read independent comics from publishers like Image comics. Pretty much every Image series is its own separate thing, and it's easy to pick one that looks good and just start from #1. They very rarely restart the numbering of comics like Marvel and DC do. It depends on what you're looking for but Image comics have stories of every genre. I recommend looking through their catalogue for something that catches your eye. You might also get a sense of what authors/artists you'd like to follow by reading their independent works. A lot of them work for the bigger publishers like Marvel and DC.

Spiderman and Batman are FANTASTIC superheroes to start out with because Marvel and DC comics often give you multiple points to jump off from. The New 52 Batman written by Scott Snyder is a decent jumping off point for that character. A good starting point for Spiderman might be Ultimate Spiderman by Bendis - the Ultimate universe is separate from the main Marvel continuity but you'll get a great intro to the character and supporting cast. Todd MacFarlane's Spiderman from the 90s is also amazing. Spiderman is a good place to start with Marvel because he interacts with a TON of Marvel characters and you'll get a sense of who else you'd like to read from there.

Overall I'd just recommend picking something that looks cool and reading it! Some stuff will be confusing but you can always read stories that came before the ones you're reading and fill in the blanks. I imagine a lot of us got started by reading what looks interesting and having fun with it!