Question

can you say how to write an invitation and give two main examples about invitation

Answer 1

If you mean by a birthday party invitations 
To, (name)
I invite you to my birthday on (date)
Ilive in (address)
Iwould be happy if you come to my party

Answer 2

for birthdays-
Dear [friend's name]
you are invited to [your name] 's [ your age] birthday party, bash
time- 
venue-
theme-
thank you!
for get together-
To [name]
we are planning a get together at [venue] on [date] at [time].
please come.
Thank you!