2.- INFORMAL INVITATIONS:

It's also common to use suggestion forms in more informal situations to invite other people to join you in doing something.

USEFUL SENTENCES:
How about + verb ending in -ing?
Let's + Verb
What about + verb ending in -ing?
Shall we + verb?
Why don't we + verb?

EXAMPLES:
How about eating out tonight?

Let's travel to Africa

What about sailing in the Pacific Ocean?

Shall we meet tomorrow?

Why don't we go to the theatre?