Er...you drag it onto the weapon you want to perform preventative maintenance on. Make sure you have at least one point of Maintenance skill in order to use it 
You might be getting mixed up broken and worn weapons though. If a weapon is jammed, you need the repair skill to get it working. Maintenance tools just raise the condition of a weapon (ie. terrible, poor etc).

You might be getting mixed up broken and worn weapons though. If a weapon is jammed, you need the repair skill to get it working. Maintenance tools just raise the condition of a weapon (ie. terrible, poor etc).