This tutorial quickly guides you how to create a new entity class and write an FGD entry. It doesn't go into much detail, because that'd require it to be 15 to 20 minutes long. Instead, that's saved for the upcoming videos. ;)
Timestamps:
00:00 - Intro thingy
00:19 - The new entity
00:38 - Creating a new .cpp file
01:00 - Required headers
01:33 - Writing the entity class
01:54 - The entity's design
02:20 - The base entity and the Use method
03:37 - Printing something to the console
04:06 - Printing what the mapper wants
04:56 - Exposing the entity class to the engine
05:08 - Why we need the FGD
05:37 - Writing the FGD entry
06:22 - Conclusion
06:58 - Outro thingy
Oh, also, I have a Discord server for my projects and troubleshooting whatever problems people might have while following my tutorials, so, yea, here's the invite if you're interested: / discord