So here are some snap shots of TortiseGIT showing how to setup your authentication.
First got to settings.
Then choose remote settings. The default is origin, here's how mine looks. Also it's easy to "add new", but it's a bit harder to remove junk, so getting it right might be handy. Or modifying an existing one instead of created several might also be handy. Basically choose your names how you want them on the first try.
Also go to the config area. Here's how mine looks. This is required to make you have your name when you check it in.
Here's the key generated by putty.
Here's how it looks in github. Note I stripped a bunch of the file out, and I added the ssh-rsa thing with the space at the end of ssh-rsa. It needs to look this way when you open the key.
After that, you should have read / write access to you account. Of course you'll have to change the jharvey stuff with your account, because you you'll only have read access to my account.