For past posts in this "series" you can go to these places: intro, Zutara, Kataang, Tokka, and Teoph. This post will be about Ty Lee and Sokka or Ty Lokka.
To be honest, Ty Lokka isn't a ship I've really thought about much even though it seems to have a somewhat decent amount of support in the fandom. Sure Ty Lee flirted with Sokka once, and he kind of flirted back, but I don't think they'd make a good couple if they actually dated. I don't really care for it at all. It actually sounds a little boring.
Why do people ship Ty Lokka?
I really don't know how to answer this question. I suppose it mostly stems from the flirting that happens in The Drill, but I can't see that in itself causing people to ship it. I guess there's just something about Ty Lee and Sokka that some people like together, but I have no idea what that would be.
I couldn't find a Ty Lokka community on fanfiction.net,so I just did a search with Sokka and Ty Lee as characters instead. I'm sure not all of these are romantic, but here you go.
Here are the results from a "Ty Lokka" search on deviantArt.
Here are the results from a Ty Lokka search on Youtube.