This Guide will explain to you how you can host a game for you and your friends playing either on a map you created yourself or on a map you downloaded from the workshop! Iam making this guide because I struggled a bit to get the hang of it myself, especially if you want to use your own maps.
Here goes!

If you want to get some maps from the workshop, just go over there and subscribe to as many as you like.
A good way to find interesting maps is to simply sort by most popular of all time, that almost guarantees that the maps have atleast some quality.
Once you've got those maps restart your game if your still ingame, and continue to step 4!

If you decide that you want to play on a map created by yourself then here's what you gotta do:
1. Create your map like usual
2. After you're done, click on upload
3. Say yes, you want to go to the steam page for your map
4. Scroll down and to the right side you should find an eye, click on there and set it to either public, if youre hosting a public game, or to available for friends if you're only playing with your friends.
After that, restart your game to be sure!

Now that you've decided on where to get your maps from you have to select them:
1. Host a game
2. Press ESC -> Game Options -> Maps
3. Tag all the maps white that you want to use, also make sure that the point CUSTOMONLINE is also white
4. Change all the other settings to your liking
5. Now your friends can join you! The maps should be downloaded automatically, if that doesn't work however, you can also send your friends the link and have them download it manually!

Thanks for reading through my guide, I hope I was able to help you!