Generate a new SSH key: ssh-keygen -t rsa -C "sheng.zhong.xie@gmail.com"

this article is based on following url:
https://help.github.com/articles/generating-ssh-keys

Generate a new SSH key

To generate a new SSH key, enter the code below. We want the default settings so when asked to enter a file in which to save the key, just press enter.

ssh-keygen -t rsa -C "sheng.zhong.xie@gmail.com"

#ssh-keygen -t rsa -C "your_email@youremail.com"# Creates a new ssh key using the provided email
# Generating public/private rsa key pair.
# Enter file in which to save the key (/your_home_path/.ssh/id_rsa):

Now you need to enter a passphrase.

Why do passphrases matter?

# Enter passphrase (empty for no passphrase): [Type a passphrase]
# Enter same passphrase again: [Type passphrase again]

Which should give you something like this:

# Your identification has been saved in /your_home_path/.ssh/id_rsa.
# Your public key has been saved in /your_home_path/.ssh/id_rsa.pub.
# The key fingerprint is:
# 01:0f:f4:3b:ca:85:d6:17:a1:7d:f0:68:9d:f0:a2:db your_email@youremail.com

Step 4: Add your SSH key to GitHub

Open the id_rsa.pub file with a text editor. This is your SSH key. Select all and copy to your clipboard.

Be warned: it is important to copy the key exactly without adding newlines or whitespace.

1. Go to your Account Settings
2. Click "SSH Keys" in the left sidebar
3. Click "Add SSH key"
4. Paste your key into the "Key" field
5. Click "Add key"
6. Confirm the action by entering your GitHub password

Step 5: Test everything out

To make sure everything is working you'll now SSH to GitHub. Don't change the git@github.com part. That's supposed to be there.

ssh -T git@github.com# Attempts to ssh to github

You may see this warning:

# The authenticity of host 'github.com (207.97.227.239)' can't be established.
# RSA key fingerprint is 16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48.
# Are you sure you want to continue connecting (yes/no)?

Don't worry, this is supposed to happen. Verify that the fingerprint matches the one here and type "yes".

# Hi username! You've successfully authenticated, but GitHub does not
# provide shell access.

If that username is correct, you've successfully set up your SSH key. Don't worry about the shell access thing, you don't want that anyway.
If you see "access denied" please consider using HTTPS instead of SSH. If you need SSH start at these instructions for diagnosing the issue