The best way really is to follow the instructions GitHub gives you:

First, go the correct directory

cd <directory of your Xcode project>

It sound like you've already got a local Git project from Xcode. If that's true, skip this code block.

git init .git add .git commit -s<type in a commit message>

Last, push into your repository. The following is copied directly from my own github account, after I created a new "test" repo. Change the "dhalperi/test" part.

Push an existing repository from the command line

git remote add origin git@github.com:dhalperi/test.gitgit push -u origin master

I was just going to leave a comment above but I will also add a summarized answer. My full answer is here.

This isn't via terminal as the question requests, but you can consider this an alternate method. It is well integrated with Xcode now, though, and not difficult to do.

Create Git repository when making a new project

See the answer I linked to above if you already have a project without a Git repository.

Make a Commit

After making a change in your project, select Commit... from the Source Control menu. You will add a short commit message.

Create a new GitHub repository

On the GitHub website make a new repository. Call it whatever you want, but don't add a README or .gitignore or license yet. After creating the new repository copy the link to it.

Add a Remote in Xcode

in Xcode go to Source Control > your branch name > Configure. Then click the Remote tab > "+" button > Add remote. Fill in your repository name and address.

Push your project to GitHub

Go to Source Control > Push. You will have to enter your GitHub user name and password the first time.

That's it. Now any time you make changes in Xcode, all you have to do is Commit and Push.

If you didn't follow this explanation, please read this and this for more detail.

Further Study

This is an excellent video that I recently watched that helped me understand Git and its integration with GitHub much better.

• The Basics of Git and GitHub

An easier way to do it in Xcode. You can even push only one current branch to GitHub or the whole project.

(for Xcode 11)

1. Just select a needed branch/(or top folder) in "Source control navigator" and right-click on it. Then select "Create remote". Or "Editor -> Create remote".

2. Then use your account at GitHub to create the repository. If using your GitHub account is not proposed maybe you still not add your GitHub account in Xcode -> Preferences -> Accounts

3. After everything is set up. Click "Create".
4. To push your project/branch to GitHub repository click "Source Control -> Push".

After that check Github. All should be there.