Useful guide above, but I can also recommend Electrum (the guide uses Mycelium and Breadwallet). Typing the key instead of scanning QR of course.
Don't forget, if you're importing the private keys into your client, to sweep the coins to a new wallet only controlled by you (that is, generate a new wallet with a new set of private keys). Fact, do this as soon as you can so you can ensure only you control those coins you bought. Your friend or someone else could still access them with those keys even if you've imported them.
I’d go to use public or private keys and then you can scan the private key onto a new wallet.
Make a wallet on your computer and send the funds across (you can check you imported the right address correctly that way). I’m sadly yet to use a bitcoin atm so I don’t know how the receipts come out.