|It is common (but not required) to have a "login profile script" that runs automatically when you log in, for the purpose of setting up your session environment such as desired variables and aliases, checking your mail, etc.|
This script will be in your home directory, and the name of the script is .profile for bourne and korn shells. Filenames that begin with a dot are called hidden files, and they are not included on a directory listing by default, but you can include them by specifying the -a option.
Do this to see all the files in your home directory, including hidden files:
The first ls command gives just the filenames. The second ls command also specifies the long option to see more info for each file, including the last modify date. The third ls command includes the u option which says to display the last access date instead of the last modify date.
If you do have a login profile script, you will see it listed, and that last ls command will show when it was last accessed, which should be when you last logged in.
Add your desired aliases to your login profile script, or create a login profile if you do not yet have one.
Then log in again so that the login profile will execute. Variables and aliases are in your "environment", and are available regardless of what directory you are in. Instead of logging in again, you could run your new profile script, but note that instead of simply running it, you would have to "source" it by putting a dot-space in front of it like:
Without putting the dot-space in front of it, it would run as a child process without impacting the current shell environment.
Also, you can create an alias at any time. Just create the alias at the command prompt, and that declares it in your current session. It would be lost upon logout, so that's why you put them in your login profile.