It has a default setting. You can set the default in your .hg file. When you pull your repo from somewhere that becomes the default. You can also specify where you want to push to.
But I'm not really sure that pushing is that much of a difficult concept, because you just have to add a remote and then use this to do your push. Not really that much of a difference...
Edit: I've just realized... I probably need to clarify the command:
The only git keywords here are "remote add". Origin could be named anything you want (call it "external"), and the git@example.com:my_project.git is actually what points to the git remote repository. You can also use the same style URI if you want to use SSH, or even HTTP(S).
for ref the equivs are:
1. hg init
2. hg commit -m "message"
3. hg branch newbranch
4. hg update branchname
5. hg merge branchname
6. hg push