There's nothing wrong with this phrase at all, Tarah. I assume from the other members' responses that it's not used in the USA, but it sounds perfectly natural to me. I, and other British English speakers, use it all the time in everyday conversation. It's a completely normal expression, and very common question here in the context of natural,informal conversation. Yes, it is equivalent to 'What did you do?' but it's friendlier and more personal. On its own, the phrasal verb to 'get up to' or to 'be up to' is often used when children get into 'mischief' (do naughty things) for fun. For example, mum gets home and sees the house is a mess, and thinks 'Oh dear, what have they been up to?' So if your friend has just been on holiday to Spain, and you want to know more about what he or she did, you'd say 'So, what did you get up to in Spain, then?' . It's a friendlier question than simply 'What did you do?'. 'What did you get up to?' means 'Tell me about all the fun things that you did!'

It's not the words that you will use if you are asking a person, Instead use these words; "What have you done or simply say "what did you do"?

Su.Ki. is right--in the US, we do use "be up to" but not "get up to." "He's up to no good" is something we might say about a mischievous child, as Su.Ki. mentions. "What are you up to?" might be used if you're suspicious about what someone is doing, or if you're just curious about what they're doing. You might say "What are you up to these days?" to someone you haven't spoken with in awhile. If you say "What did you get up to?" to an American (like my European colleagues sometimes say to me), for example to ask about a trip, I think generally we'll understand. However, we'd probably say something like "What did you do (there)?" as others have mentioned or "How was it?" instead when we're speaking.

This is not correct language though a lot of native English speakers will say it. " What did you get up to?" simply means "What did you do?". I wouldn't use "what did you get up to?"