Hello *your friend*,
I am writing to invite you to an event. The name of the event is: Exhibition of Modern Art. That is a wonderful exhibition, you should come there. Are you free on Saturday morning? The event will start at 9 o'clock in the Arts Centre. So let meet at 8:15. Then we will have 45 minutes to meet and prepare to watch the exhibition. I hope that we'll have fun and expand our knowledges. This is enough for my letter. Goodbye and have a nice day!
(Love/ Best Wishes /Cheers/ Looking forward for you)
*your name*