Step one: Unpack the box, remove all the parts and the frame from it. Check that everything is unwrapped and accounted for. Don't rest the bicycle on some sensitive parts like gear sprockets or derailleur so that they won't warp or bend.
Step two: Take bicycle lubricant and squeeze it on the front wheel axle. The front wheel position should be between the front brake pads. Then slide the axle in, change the spring and cap, and tighten.
Step three: Do the same procedure with the rear wheel, and then lightly pull up on the chain, installing it on the gears' teeth.
Step four: Take an air pump to inflate both tires. The recommended pressure is printed on their sidewalls.
Step five: Place the seat post in the seat post tube, and then tighten the clamp. Be certain that the seat is aligned with the frame's top bar.
Step six: Slide the handlebar stem in the vertical handlebar tube. Adjust their position until they are perpendicular to the front wheel. Tighten the neck using an Allen wrench. Pay attention not to loosen the headset too much, or else the handlebar nut could drop into the tube.
Step seven: Find a pedal marked with "L," and screw it into the left crank. Do that by rotating the nut counter-clockwise using an adjustable wrench. Repeat the same procedure with a right pedal, only this time you screw it in clockwise.
Step eight: Reconnect the brakes and double check all the screws and joints. They must be tightened before taking off on your new bicycle.