Trusses, Domes and Arches are three different types of structural elments. Basically all three can be used to cover large spans.
A Truss can be visualised as a long beam if you look at it, truss as a whole but composed of web members in various shapes. The resistanace offered to loads by the members of the truss is mainly in the form of axial forces. This can be essentially viewed as a one dimensional elsmet, the turss as a whole. Trusses are spced at certain intervals to cover larger areas perpendiculr to the span of the trusses.
Domes too serve for larger spans with their unique architectural appearance. Shells/Domes are two dimentional elements of various shapes (sperical/hemi sperical, paraboloids, hyperbolic paraboloids etc). Due to their unique shape the resistance to the loads is by compression. These are normally constructed by concrete, since it is good in compression and can be moulded easily to any shape. However the difficult part with the domes is that the cost of construction higher because of complex forms.
Arches in the other hand nothing but ordinary beams curved in shape. These too because of their shape attract comprssive stresses.
