You don't have to, it depends on the sentence for example this sentence doesn't need a comma:
Robert Louis Stevenson wrote Treasure Island.
no. if but before is a sentence on its on and after but is a sentence on its own then put a comma before but.
Put a comma
'Sincerely yours, [insert name here]'
No, a comma is not needed after "yes" when starting a sentence.
Should you put a comma before a person's name that comes at the end of the sentence, Miss Smith? A comma represents a slight pause. Speak your sentence with and without a pause just before the person's name. As you can see, a slight pause belongs there. Therefore, a comma belongs there. The purpose of punctuation is to make your sentences more readable. A comma makes the sentence more readable and easier to understand when spoken out loud. The two are almost one in the same.
No, you do not need to put a comma after "To begin with" when it is used as an introductory phrase in a sentence.
no but sometimes after the name
Typically, a comma is not used immediately after "though" in a sentence. However, if "though" is used as a conjunction at the beginning of a sentence to introduce a contrasting idea, a comma may be used after it.
Yes, you should put a comma after "welcome" when addressing someone by name. For example, you would write, "Welcome, John." The comma sets off the name from the rest of the sentence, following the rules of direct address in English grammar.
No.
Sometimes. It depends on the sentence.
You can put a comma before or after just about any word if the sentence structure requires it. If the sentence structure does not require it, it may be permissable to use a comma to assist in clarity and avoid confusion. Otherwise, don't use a comma. Have I confused you yet? Using a comma does not depend on the word, it depends on the structure of the sentence.