You can easily create an SSH key pair by using ssh-keygen as in the following example.

$ ssh-keygen 
Generating public/private rsa key pair.
Enter file in which to save the key (/home/user/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/user/.ssh/id_rsa.
Your public key has been saved in /home/user/.ssh/
The key fingerprint is:
1a:6c:a4:94:df:e0:19:ec:85:b0:3f:27:e4:a1:de:65 [email protected]
The key's randomart image is:
+--[ RSA 2048]----+
|                 |
|   .             |
|    o E          |
|     O o         |
|    c @ S        |
|   o A @         |
|    . E .        |
|   . =           |
|    .            |

There are a few things that you might want need to take note;

  1. A 2048 bit RSA key pair will be generated by default. You can use different key type by using -t option and specify any of the supported key types

    dsa ecdsa ed25519 rsa rsa1
  2. The private key will be stored in ~/.ssh/id_rsa while the public key will be stored in ~/.ssh/ You can specify other location when prompted during the key generation process if you already have a key pair at the default location
  3. You can specify passphrase for your key pair when prompted but you’ll have to not set the passphrase to use passwordless SSH login