Do I have to wear AMD FreeSync or can I skip it? For Fortnite stop
You can of course leave that out.
What makes the difference
Wants to get as many FPS out as possible
AMD FreeSync ™ Technology is an AMD initiative that leverages industry standards such as DisplayPort ™ Adaptive-Sync to deliver dynamic refresh rates to end users. With AMD FreeSync ™ technology, the refresh rate of a display is synchronized with the frame rate of FreeSync compatible graphics cards. This reduces or eliminates visual artifacts that many users find particularly annoying: input latency, image distortion, and stuttering in gaming and video playback. AMD FreeSync ™ technology can be delivered over DisplayPort and HDMI® connections.
You can have it on or off, it doesn't matter.
Can omit
This will give you at most 2 to 3 FPS more, I would have it activated, unless your FPS rates are around 20 or less
What that is is well explained here
If the monitor can Freesync. Then turn it on. You do not have to. If the monitor has no freesync, you can't turn it on at all xD