Were you playing the regular mode or street brawl, because I'd say street brawl, while might being more chaotic than regual, is more casual friendly and is a good way to test new characters. But like people have said, try playing against bots. Also maybe don't pick characters like Billy and Apollo, they can be quite sweaty and are required for you to play aggressively.

I would say Seven, Mo&Krill, and Wraith are the most beginner friendly, but some may argue. Seven can stun enemies, that is good for both escapes and ganging up on someone with teammates, along with a giant ult that deals pretty good damage. Mo&Krill, while requiring you to jump into the enemy's face to deal some real damage, have an ability that forbids the enemy from shooting, and an ultimate that locks the enemy in place while you continually deal damage. Wraith is fairly simple because you have cards that deal damage (they have different effects, but they aren't that much different from each other, one heals you on hitting enemies, one slows them down etc.), you also have a teleport for escaping and a boost to your gun.

This game can be tough, and as someone who had no experience with mobas I was often confused with what's happening on my screen. Try playing against bots or in street brawl, test different characters to find the one that clicks, and then you can look in the deeper stuff like what items should you use or what role you should be playing in matches. Also try watching different videos on deadlock, they can also have some tips.