Teams on Pokemon Showdown! are stored in your cookies. If your teams aren't saving, change your browser settings so that it doesn't clear your cookies. Alternatively, back up your teams once you make them on Notepad or a similar program.
I have a video tutorial on my youtube channel. I made that in 4th gen but I still use the same method of making pokemon videos. After you watch that, If you have any other questions you can leave a comment, or leave me another VM here.