Definition of Invitation
Invitation is a way to invite someone or more to go a place or to do something. The function of invitation is to ask some one to go to a place or to do something.We usually use the “invitation”  in our  daily life, for example if we want to hold an event like a birthday party . We use the invitaion and if we want some one to do something , like if we want our friend to help us.We use the invitation too. 

Invitation use simple Present tense.There are too kinds of the Invitation, that are from invitation and inform invitation. 

Invitation also has general structure of invitation are    : 

Ø What Event 

What event is what thing that 

Ø Who 

People that`s we want to invite 

Ø When 

When is the time when the event is held 

Ø Where 

Where is the place where the event is held

Formal Invitation

Formal invitation is usually originate from institute, companies and a kind of it. Normally formal invitation is written invitation.
Informal Invitation
Informal Invitation is personal invitation given to a friend, family, etc. Informal can be written invitation and verbal invitation.
If we want invite someone we can use:
∞ I would you like…?
∞ Can you go to…?
∞ Could you go to my home…?
∞ Shall we…?
∞ I’d like invite you to…

To accepting an invitation:
∞ I’d like to…
∞ That sounds great
∞ Thanks for your invitation
∞ I’d be glad
∞ That sound like fun
∞ It’s very nice of you to invite me
∞ It’s sounds interesting
To refuse/Declining an invitation:
∞ I’d love to, but I can’t
∞ Sorry, I’m really busy
∞ I’d love to but I don’t think I can