Newbie question - encrytion keys

I am using outlook express and my emails are not encrypted going out. When I hit send there is no option to do anything, the email is just sent.

I was told by another that I need to send my key to receive encrypted email? I have an email certificate that I stored, but I don’t know what or where there is an associated number.

Can someone explain how I am supposed to send and received encrypted email.

Thanks.