Inside ,where the wire spool goes , there are two lugs, bolts, or terminals, (whatever you want to call them).....they have nuts on them....one is marked positive and one is marked negative....For flux core wire, your electrode (gun you hold in hand) the end of the wire should go to the negative post....And the ground clamp you clamp on to the piece you are welding, that end should go to the positive post......BUT, when using solid wire with gas they are supposed to be reversed....your electrode end should go to the positive terminal inside the welder and the ground clamp end should go to the negative terminal.... Different brand welders may use different techniques to change polarity but you are just swapping around the positive and negative between electrode and ground
