Where the template says Trim Area, that is your page size. So in the Width and Height fields, type in:
W = 255mm
H = 360mm
ID will convert the units. you can change the units for both W/H later by right clicking on the ruler and choosing millimeters if desired.
Where the template says Bleed Area, that is the top set of boxes at the bottom of the page setup dialog. So...
W = 5mm
As long as the chain link is depressed as in your screen shot, the 5mm will populate the others.
Where the template says Type Area, that is the margins setting which is the second section from the bottom. The template uses odd values, so to me the easiest method is to leave the Chain link depressed and type in:
Now click on the chain link. This means that you can alter the Inside and Outside margin values. Type 7.5mm in the Inside entry box, hit tab, type 7.5mm in the Outside margin entry box.
That should be it.