In an IM you are actually having a conversion.
In an email you have to wait until someone writes back to you.
Which usually takes a day.
Instant messaging is more like a telephone call
And Email is more like mail.
With instant messaging you can only send a message when the person is online.
With Email you send a message any time

There are some sites that let you play in real time.
You can play checkers with someone on the Internet
Just like you were sitting right next to them.
Others are turn-based. You make a move and wait a day
for the opponent to move.
In a real time game site, you can see the pieces moving.
In a turn based game site, you have to click on refresh to see if someone moved.