There are a lot of unknowns here. What mail client are you using?
Mutt, Elm, and "mail", sup and Alpine are probably the most common ones.
imap normally keeps mail on the server. pop3 normally downloads mail to the client.
The commands are different for the kind of mail server, and which client you re using.
At it's simplest,
You would just type "mail", and it shows you a list of emails stored in your client.
Press "1" to view message 1. Press "d" to delete this message. Press "q" to quit.
But this just "displays" the contents of the email. Is that good enough?