items (information) in an invitation: what should be contained in an invitation? At least the following points should be necessary.
--what for : the event or activity
--when to come : time
--where to go: place
--how to get: ways to meet or get to the place

response to an invitation
after receiving an invitation, there must have response to it. Without any exception, there are three possibilities: --accepting—declining and --showing uncertainty

after getting the basic knowledge of invitation, let’s come to focal point 2: informal / spoken / oral invitation. In this part, we will learn common expressions used in spoken invitation, accepting a spoken invitation, declining a spoken invitation and common expressions used to express uncertainty.
These expressions are quite useful and once you grasp them it will be beneficial for your later following study, so just put your heart on them and try to bear them in mind.

---Would you be able to __________? Come to my birthday party this evening
---I would like to invite you to _____. My wedding next Sunday
---May I invite you to __________? Be present at our debate
---How about _______________? Going to a ball tonight
---I wonder if you could _________ care to go on holiday with me
---Would you like to ____________? Have a cup of tea with me

common expressions used in declining a spoken invitation
---I’d love to, but________________ you see, my uncle is taking me out for the day
---Thank you for the invitation, but_____________ I am occupied at that time.
---That’s great, but I’m afraid__________ I am not free then.
Next, let’s study an example of informal invitation. This dialogue is about two guys discussing some activity. Please pay attention to those common used expressions in invitation.

OK, it is your assignment to make such dialogue by using some common used expressions in invitation.