running multiple threads at once?

EDITED:

hey,
im trying to create my own gamemode, and one of the problems I have is trying to delete my crates in one thread from a completely different one. When I use the "waitill" command, it stalls up some other threads I need to run. So are there any other ways to delete crates from other threads besides "waitill"?

and the same HUD elements from other threads? Like if i create a progress bar in one thread, then I try and make a conditional statement in another thread to delete the progress bar, I get an "uninitialized variable 'progress bar'" error. Any way around that without using "waittill"

Use the entity. prefix on any variables to access the thingy from any thread.

Example:
/marked as solved

If you need to ask anymore questions or need something to be cleared let me know otherwise, tell me to close the thread.