Option 1 You're inviting your friends to a formal dinner party at your place.
Include: the date, that it's for your birthday, the dress code, the address and who they should contact if they have allergies.
You're writing to your friend Jessica Williams.
Option 2You were invited to watch a football game of your favorite team in a sky box. You're accepting the invitation and bringing a friend.
Include: a thank you, which friend you're bringing, ask what time you have to be there, where it is and what the dress code is.
You were invited by Jack McConnor.