Fellow, Unix guru's

Need help customizing my bash shell
with alias commands everytime I set a alias ex: alias ll= 'ls -al'
the next time I log in at school I have to reset it again
I have search my textbook "Guide to Using Unix"
and it does not speak on it all.

OS: Redhat Linux 7.4.2

How can I make aliases stay in me bash shell even when I logout
thank ahead of time.