[klondike98]

Just because the tube lights up (i.e. the filament is working) doesn't mean it is working correctly, but its a start.  It won't work if the filament (which is sort of like the filament in an incandescent light bulb) is burned out.  You can check the filament by putting an ohm meter across the filament pins.  To find out which pins are the ones to check you look up your tube on a database like this one (there are others).  If you measure a resistance (usually an ohm or two) the filament is probably OK.  If there is no measurement, i.e. there is infinite resistance, the filament has burned out and broken.  Some quick vacuum tube reading.  There are vacuum tube testers that will tell you if the tube is performing well or not but that's a purchase you probably want to wait on to see if you become addicted to this sport