Extruder is Clicking - Won't Accept Filament or Print!

[MeoWorks]

The clicking is happening when the filament is slipping on the hobbled bolt's teeth. Eventually it'll grind into the filament and all extrusion will stop. Depending on what extruder you have, you should look into either tightening or loosening the idler or upping your temperature or slowing your print speed.

If it's a clog, just bring the hot end to 180C, unscrew the nozzle and clean it out. Acetone dip will eat ABS and burning will crystallize PLA and make it easy to scrape out.