So, now you have a wallet and you've got some bitcoin- and you want to try making a purchase with it. Now what?
First, you need to find a place in your area (or online) that will accept Bitcoin as a payment method. For this I recommend the Airbitz Merchant Directory.
Unlike a credit or debit card, where you give someone your card number and they use it to "pull" money from your account, Bitcoin works the other way. A bitcoin payment is a "push" transaction, which works a lot like sending an email. This makes it a lot more secure and less cumbersome for online merchants to support than credit cards, since no customer account numbers have to be kept on file and no complex security measures have to be put in place to keep them from getting stolen.
In order to spend bitcoin or send it to someone, you'll need to know the address to send it to, and enter it in the "send to" field of your wallet. A bitcoin address is a very long string of letters and numbers, and usually has a 1 at the very beginning. (if it's a multi-signature wallet address, it will have a 3 instead.)
Your average Bitcoin address will look something like this: 1ETBbVWLTuMbQNErtt1nhEo8xiGHZpmZvm
Unless you're on a computer and can easily copy and paste the address, remembering all those numbers and letters (which are case-sensitive, by the way) can be a real pain- and the address for a payment is something you really don't want to get wrong, because Bitcoin transactions are irreversible. So all Bitcoin wallets have the ability to generate a QR code of the address, like the one in the photo at the top of the page, and a mobile wallet has the ability to scan them built in. This speeds things up quite a bit, especially if you're at the computer and want to use a mobile wallet to pay for something.
Some newer mobile wallets, like the Airbitz wallet, also have the ability to transact through a Bluetooth connection, which helps in a lot of situations since a cracked phone screen or glare from a bright light source can sometimes make QR codes hard to scan.