An invitation is a request to come and take part in a major event, usually an official one. It should express respect towards the person and it should be original.
It is often written on a decorative note cards. You can come across with the invitation sent by letter or via an email.
Composition
Place, date (optional);
Header;
The formula of the invitation (e.g. “You are welcome”, “We invite cordially”);
Information who is invited;
The occasion of sending the invitation;
Give specifics as to when, where and at what time the ceremony is to take place;