Ok, so your new to bitcoin. The first thing you will need to do is chose a bitcoin wallet. This is typically software that you will download and run on your computer, smartphone, or a website you log into, or all three maybe.
There are hardware wallets and paper wallets also, but I will not go into those at this time. Why not?
Because hardware wallets cost money, at the time of this writing I believe they are $90 and up.
As for paper wallets.. well quite honestly I do not know all the details of how they work… I believe they consist of one of those new square barcodes and require that you know the passphrase, and the person whom you would do any kind of transaction with would have to have a smartphone and software on it and a internet connection to get any transfers done.
So, as far as picking wallet software goes, first of all you need to make sure the software you choose has all the features you will need. This is why I think something like coinbase.com is the best choice, as it can link to your bank accounts so you can actually sell your coins directly and get cash quickly. If you choose something like greenaddress, you will have to transfer your coins somewhere else first before you can get cash for them, and you will pay quite a bit in fees to do this. So best to avoid all the unnecessary transfers and the fees that go with them.