Step 1: Opening.
I hope this letter finds you in the best of health and spirits. With Diwali approaching, I am eagerly waiting to celebrate it in my native place.
Step 2: Invitation.
I would be delighted if you could come to my native place during the Diwali holidays. The festival here is celebrated with great joy, decorated houses, bright lamps, sweets, and fireworks. It will be a memorable experience for both of us.
Step 3: Closing.
Please do come and spend this Diwali with me. Convey my regards to your parents. Looking forward to your positive reply.
Yours lovingly,
ABC.

formal Letter Write a letter to the Manager, Youth Club, Pune, requesting him/her to send the details of fees, concession, food and other facilities.
Make enquiry in detail about it.
Add your own points.

Informal Letter Write a letter to your friend informing him/her about this summer camp. Ask him/her to join this summer camp. Tell him/her the usefulness and advantages of this camp.