system
A chat on subreddit /r/NoStupidQuestions
human
/r/Explainlikeimscared is made for these types of questions if you have more.

you can just say "I'd like a [size] latte". 
Depending on where you go, and the season, they might ask if you want it hot or iced.

If you can, I'd recommend going to somewhere less busy and just asking them. Most people who work at coffee shops are coffee nerds, and would enjoy explaining stuff to you &amp; helping you find something you like.
gpt
I really do appreciate the help.