You just need to fill the system from the reservoir and the bleed all the air out of the system. You can start with the bleed nipple on the caliper loose so that air and fluid can come out of it. Slowly feed fluid to the reservoir and pump the brake lever (slowly so the fluid doesn't squirt upward all over the place). When fluid starts coming out of the bleed nipple you need to put a plastic tube on it and put the other end in a glass jar. Keep pumping fluid into the system being careful not to suck air into the piston at the master cylinder.
When pubbles stop coming out of the plastic tube the system may be properly bled of air. It will help to close the bleed nipple before releasing the brake lever to prevent air being sucked back into the system. When no bubbles are being pumped out close the nipple and try the brake. If properly bled the lever will feel hard and will not travel too far toward the handlebar. If there is air in the system, the lever will travel all the way to the handlebar with little resistance and no braking action.
Cover the paintwork on the bike with plastic to keep any spillage off the paint. Brake fluid eats paint.
2004 Rebel 250, 2003 BMW K1200GT (roadburner), 2004 BMW R1200GS(all purpose),
1996 Ducati 900SS CR (California Bike), 1973 Norton Interstate (in a box in the basement)