speaking of the past: "Ich war mal in China" here it's a shortened form of "einmal". -> I've been to China once. speaking of the future: "Ich würde gern mal nach China" same here, in English I'd say: -> I'd like to go to China someday asking for something: the word "mal" makes it sound extra casual and implies that it's just a short task you're asking the other one to do. "kannst du hier mal mit herlangen?" roughly: can you lend me a hand here? "kannst du das mal halten?" can you hold this for a second? "kann ich mal deinen Stift haben?" can I borrow your pen for a very short time? (like for subscribing a document)

"time(s)" in this case. einmal = one time zweimal = twice dreimal = three times viermal = four times etc.