Beginners Gitters and Character Help

The only D&D experience I have was one evening playing casually with a bunch of friends. When we played my DM essentially built my character and I just told him what I wanted to do. I have no experience with serious character building and I'm really nervous to apply for a game without having a solid character already made. The character my DM and I made was a custom warlock with a few tweaks on existing spells, and I'm really attached to him but I don't know how people on Roll-20 feel about custom classes. If anyone can help me build a character that doesn't suck I would appreciate it a lot. Also just looking to meet some cool people in this community so I don't feel so nervous about making applications for games in the future. 

If you join a game, its very likely the GM will require you to make a character specifically for their game, and may have specific house rules or restrictions on what you can play. Also, there are many more players than GMs all applying for games, so you are essentially in competition with a lot of other players for a slot in a game. Some GMs will specifically advertise that they are willing to help new players, but the rest will assume you know what you need to know and will reject people that are going to need too much hand-holding. So the best thing to do would be to figure out how to make a character in the system you want to play (online character designers and SRDs exist), and be open minded about playing new characters that fit what the GM wants for their game.

I just got done applying for some new games. I looked up YouTube videos about character building and such, so hopefully when the time comes I will be prepared. Thank you for your advice, and hopefully all works out!

Good luck!