It is of vital importance that the mechanism and joints are not subjected to any stress during these procedures. These are delicate areas and can be expensive to repair. Therefore, do not take the flute out of the case by its mechanism.

Hold the body by the barrel (headjoint socket) and the headjoint around the tubing below the lip plate.

Keeping the headjoint in line with the main body, insert the headjoint into the main body using a careful rotary action.

Place the footjoint in the palm of your hand, and hold the main flute body around the headjoint socket.
Holding the two parts in line, join the two sections together with a carefull rotary action. Should you need to get a better grip on the footjoint then place your thumb on the low C and/or C-- key cups.

Do not hold any other footjoint touchpieces as they can easily become damaged. To disasemble the flute carefully reverse the above procedures.

Courtesy of http://www.worldwind.co.uk/