How do I add tags to my threads?

[London Parris]

I'm seeing people add tags to their threads. I just want to know how to do it myself.

 

[Fanny]

Click on the tag symbol.

 

[Koops]

I seem to have a problem with the amount of maximum tags I can tag a thread with. I could put 5 on my ask thread before but for some reason now it only lets me have 3.

Does it have to do anything with the character limit?