While the EGit plugin for Eclipse is a good option, an even better one would be to learn to use git bash — i.e., git from the command line. It isn’t terribly difficult to learn the very basics of git, and it is often very beneficial to understand some basic operations before relying on a GUI to do it for you. But to answer your question:
First things first, download git from http://git-scm.com/. Then go to http://github.com/ and create an account and repository.
On your machine, first you will need to navigate to the project folder using git bash. When you get there you do:
git init
which initiates a new git repository in that directory.
When you’ve done that, you need to register that new repo with a remote (where you’ll upload — push — your files to), which in this case will be github. This assumes you have already created a github repository. You’ll get the correct URL from your repo in GitHub.
git remote add origin https://github.com/[username]/[reponame].git
You need to add you existing files to your local commit:
git add . # this adds all the files
Then you need to make an initial commit, so you do:
git commit -a -m "Initial commit" # this stages your files locally for commit.
# they haven't actually been pushed yet
Now you’ve created a commit in your local repo, but not in the remote one. To put it on the remote, you do the second line you posted:
git push -u origin --all