once you get the hang of it, it gets more fun,you can line them with matching paper that you used on the card. I actually made my first one by taking an old envelope apart and making a cardboard template, I used a ruler, my cutter and a scoring tool ,plus a bone folder. good luck.
I also started by tearing one apart and using it at a template. Then I made my own templates from chipboard. That worked for years until I finally bought MS scoreboard. I love it. I love making boxes too.
I hate making envelopes so I go down to my local dollar store and buy the excess envelopes they get from selling cheap greeting cards. They usually come really cheap and every colour of the rainbow. Just ask the teller.
I've been wondering about making my own envelopes. I thought to just wing it... but I'm worried that learning to make my own envelopes will result in creating cards of various miscellaneous sizes, and then I'm not sure how that will affect the amount of stamps required for postage. Lol