An envelope is a paper pocket, and people put letters in it.

First, we should write a letter, then put it in an envelope, and finally put it in the mailbox for mailing.

First, I will write a letter, then put it in an envelope, and finally, put it in the mailbox and send it.

I'm glad to help you. I hope it helps you.

If you don't understand, please keep asking questions. If you are satisfied, please adopt it. O(∩_∩)O Thank you.