When it comes to filling a butane lighter, there are a few things you need to know. Butane is a gas, and as such, it needs to be treated with care. The first thing you need to do is make sure that the area around the butane canister is well ventilated.
Next, locate the valve on the canister and open it up. Slowly start pressing down on the canister until you hear gas hissing out of it. Once you hear this noise, stop pressing down and quickly attach the hose from the butane canister to the filler nozzle on your lighter.
From here, simply hold down on the filler nozzle until your lighter feels heavy in your hand - this means it's full. Make sure not to overfill it, as this can cause problems later on down the line. Once you're done, disconnect the hose and screw the valve back onto the canister tightly.