Accepting the pull request is not something you do, it is something done by the repository owner. It is the next step though. When the original repository owner logs into their account, their Newsfeed shows your pull request. It also shows your fork from a few days earlier. For example:

The repo owner can click on the request and see your full request. An owner can Merge, Edit, or Decline a request. Owners, and others with access to the repository can Approve a request. Clicking Approve simply means the approver reviewed the changes in the pull request.

You'll get an email when your pull request is accepted. For now, continue onto the next section.