Find out who's metal it is and then get their techincal details or manual...... If you don't understand, either ask for help or get someone who does it regularly to advise and help........ don't take a risk and don't make a mistake if you don't understand!! This is the first part of a wall - if the wall if built and then fails - it will cost you dear to start again...
A deflection head detail is how you allow for movement of the floor below and slab above (in commercial buildings, the floors are usually canilevered from a core and will deflect, sometimes a lot!). The detail to allow for this movement also takes into account sound and fire integrity of the wall..... so it is important that it is built properly!