If you mean writing the Letter Of Explanation (like the cover letter), you don't need to write all what you've said because the information should have been provided/attached in the different categories.
"A person has invitation letter from his friend"
>> Obviously you need an invitation letter.
https://www.canada.ca/en/immigration-refugees-citizenship/services/visit-canada/letter-invitation.html for format
>> This statement "He will stay with his friend who will provide him free accommodation" should be on the invitation letter your friend will provide. This will be attached on the
Invitation category
"he has also sufficient funds around $ 10,000 CAD in his account"
>> This can be seen on your bank statement as you need to attach 4 months of bank statement on
Proof of Means category
>> On the
TRV form you need to indicate how much funds you will bring/spend in Canada.
"to visit different places describing the places to visit."
>> You need to provide a day to day itinerary of the places you will visit and activities and attach on the
Purpose of Travel category
Instead of describing the places to visit and what you have (letter of invitation, 10K), make the letter direct and focus on
why you will visit Canada. Yes you can say that you want to meet your friend and also for tourism purpose. Better indicate
why you need to visit your friends and why you want to see the tourist spots in Canada.