INSTALL GIT ON YOUR SYSTEM
Go to your web browser and then install git using the link below and follow the process.
On installing it will also install git bash
https://gitforwindows.org/

Go to your command for those using Macbook and the windows key for those using windows and type git bash and then open it

Generating the SSH Keys
so before you generate a new SSH keys, you have to check if there is an already available SSH keys which you may have installed a long time ago by running this line of code

ls -al ~/.ssh

After running the command it will show the list of available private and public keys as shown in the image below

if not available, then you can run this command

ssh-keygen -t rsa

when asked for the location to save the keys accept the default location by pressing the enter key.

By default the git bash recognizes your personal Github account, you can check that by running the command

git config user.name

git config user.email , to check the username and email .

After generating the SSH keys for your personal github account, you can do the same for the work account or any other account using the command line below

ssh-keygen -t rsa -C "email@work_mail.com" -f "id_rsa_work_user1"

so the "email@work_mail.com" is your work email, the one you used to create the work github account or whatever email you used.
and "id_rsa_work_user1" is your username on github, so it distinguishes between the personal and the work SSH keys

So by now we have two different SSH keys
~/.ssh/id_rsa
~/.ssh/id_rsa_work_user1

Adding the new corresponding SSH key to your Github account
Copy the public key pbcopy < ~/.ssh/id_rsa.pub and then log in to your personal GitHub account:

To see the key on git bash, enter this command

cat ~/.ssh/id_rsa.pub
cat ~/.ssh/id_rsa_work_user1.pub
N/B: id_rsa.pub is the name for your personal SSH key and >id_rsa_work_user1 is name for your work SSH key or the name you used to save it, if it is your username, that's how it will appear

a. Go to Settings
b. Select SSH and GPG keys from the menu to the left.
c. Click on New SSH key, provide a suitable title, and paste the key in the box below
d. Click Add key — and you’re done!

Then do the same thing for your work Github account, if successful github will show a prompt message that you have successfully added your SSH key.

Registering the new SSH Keys with the ssh-agent
Ensure the ssh-agent is running by inputting this command
eval "$(ssh-agent -s)", and will show something like this "Agent pid 1280"

Then add the ssh-agent like this :
ssh-add ~/.ssh/id_rsa
ssh-add ~/.ssh/id_rsa_work_user1

if successfully added it will show something like
identity added : path to where it was added

To check the list of SSH keys in your computer, you can run the command

ssh-add -l
And it will show the list of keys

Creating the SSH config File

$ cd ~/.ssh/
$ touch config // Creates the file if not exists
$ code config // Opens the file in VS code, use any editor

so this creates a mark down file in vs code then you input this values
N/B: make sure that there is no comment else there will be an error

Host personalemail@gmail.com
HostName personalemail@gmail.com
User github username
IdentityFile ~/.ssh/id_rsa

Host workemail@gmail.com
HostName workemail@gmail.com
User github username
IdentityFIle ~/.ssh/id_rsa_work_user1

One active SSH key in the SSH agent at a time **
so as I mentioned above you can use **ssh-add -l to see the list of SSH key in your system or computer. Then you can use ssh-add -D to delete all the keys, then you can add them one by one by using this command in accordance with the github account you want to use at the moment be it personal or work
for personal ssh-add ~/.ssh/id_rsa
for work ssh-add ~/.ssh/id_rsa_work_user1
N/B: "~/.ssh/id_rsa" this is the path it was stored in your computer

The ssh-agent now has the key mapped with the personal GitHub account, and we can do a Git push to the personal repository.

To push to your work GitHub account, change the SSH key mapped with the ssh-agent by removing the existing key and adding the SSH key mapped with the GitHub work account.

Setting the git remote Url for the local repositories
Once we have local Git repositories cloned /created, ensure the Git config user name and email is exactly what you want. GitHub identifies the author of any commit from the email id attached with the commit description.

To list the config name and email in the local Git directory, do git config user.name and git config user.email. If it’s not found, update accordingly.

git config user.name "User 1" // Updates git config user name
git config user.email "user1@workMail.com"
git config --globe user.name "User1"
git config --globe user.email "user1@workMail.com"
N/B: This will add the username and email to the globe

While Cloning Repositories
Note: The next step will help, if we have the repository already available on local.

Now that the configurations are in place, we can go ahead and clone the corresponding repositories. On cloning, make a note that we use the host names that we used in the SSH config.

Repositories can be cloned using the clone command Git provides:

git clone git@github.com:personal_account_name/repo_name.git
The work repository will require a change to be made with this command:

git clone git@github.com-work_user1:work_user1/repo_name.git
This change is made depending on the host name defined in the SSH config. The string between @ and : should match what we have given in the SSH config file.

so for an example I was able to clone the repo of one of my favorite developers JONAS SCHMEDTMANN by using the steps stated above

For Locally Existing Repositories
If we have the repository already cloned:

List the Git remote of the repository, git remote -v

Check whether the URL matches our GitHub host to be used, or else update the remote origin URL.

git remote set-url origin git@github.com-worker_user1:worker_user1/repo_name.git
Ensure the string between @ and : matches the Host we have given in the SSH config.

If you are creating a new repository on local:

Initialize Git in the project folder git init.

Create the new repository in the GitHub account and then add it as the Git remote to the local repository.

git remote add origin git@github.com-work_user1:work_user1/repo_name.git
Ensure the string between @ and : matches the Host we have given in the SSH config.

Push the initial commit to the GitHub repository:

git add .
git commit -m "Initial commit"
git push -u origin master

if this article was helpful please share and comment your thoughts on it.

Reference from Bivil M Jacob from his freecodecamp post, and Jonas Schmedtmann from his complete javascript repo