This page should contain information about how to work with [https://git-scm.com git], specifically from the point of view of someone familiar with [https://subversion.apache.org Subversion].

To start:
{{{
svn checkout https://svn.macports.org/repository/macports/trunk/dports
}}}
becomes 
{{{
git clone git@github.com:macports/ports.git
}}}
When you clone you will get the entire history of the ports tree, with the latest version being checked out in the filesystem.
After you make a change, you can run {{{ git status }}}
and get something like this.
{{{
On branch master
Your branch is up-to-date with 'origin/master'.
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

	modified:   aqua/iTerm2/Portfile

no changes added to commit (use "git add" and/or "git commit -a")
}}}
What this tells me, is that I've changed a Portfile, but not done anything.
After that, you can add the files that you want to add to your commit using {{{git add aqua/iTerm2/Portfile}}}.
Now, {{{git status}}} will look like:
{{{
On branch master
Your branch is up-to-date with 'origin/master'.
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

	modified:   aqua/iTerm2/Portfile
}}}
Then run {{{git commit}}} and everything is set. On your machine. To push to github you then have to run {{{git push}}}.