How to start dating in your 20s

This has been a subject I've avoided up till now, but it bothers me because I would like to see whether I even enjoy dating... Plus I could use a friend.
I have never dated anyone before, casually or otherwise, and kind of missed out on the college trying new things period. I guess I've always been shy, and very academically focused. Dating or flirting always seemed like extra. Not a priority.
But now I'm starting to worry... what am I even doing? I have found myself flirting with co-workers in the past, sort of out of curiosity as to whether I could flirt with anyone. Not a great place to pick someone up though.
I just seem to be either too serious, or too careless; too focused on work or projects or bettering myself, or just climbing out of depressed moods, to bother with the work of getting with someone.
I don't like small talk. I get too serious and I love debates, though I also used to be sort of fun with my old friends.
And then, I wonder if I'm ready for any relationship at all, when I keep falling into depressions, and my life seems really flimsy right now. I don't think I want a boyfriend, but I don't know how to do casual dating... help!

Except for the depressions, I feel you. I don't really go on dates. I don't know how to ask and I haven't been asked. I mean, I have gone out with boys after we started hooking up, for a beer or dinner, but it never felt like a date. Even had a friends with benefits the last year of high school whom I used to dine out with, none of us had any feelings though so it was all really casual. Therefore I don't really know how to date, how to act on a date, what is expected etc. I think if someone asked me I would just screw all those rules and be me - eat what I wanted, preferrably pay for myself (I hate it when others pay, feels like I can't order what I want), and not just talk about boring subjects. I don't know. I have ever really either been casual/single or in a relationship, going on a date with someone you're not serious with seems weird to me, if I went on a date with someone, would it mean I was interested in them? These things makes me wonder if I would dare to say yes if asked :P

Yeah, I would act weird on a date. Actually, I have been out on a few formal dates, but it wasn't something I really wanted. The guys asked me and I wasn't into them but I was flattered so I went. I talked too much, didn't learn anything about them, discovered I wasn't particularly attracted to them, felt patronized when they wanted to pay (and annoyed that we had gone to a pricey restaurant...as strangers)
For me, I just don't know how to be casual. I guess I'm afraid of being taken advantage of in some way... I'd want to get to know someone as a friend first... Or at least feel powerful enough to decide what happens. I overthink things a lot.
I guess to really formally be dating, for me I would want to be friends with the person.