All attributes are described in the documentation (here as an example for the box). The two most important ones are the position and the rotation  as well as the height, width and depth.

Position

The position of a primitive or entity is based on the 3D space with the coordinates x, y and z in the following manner. You can use your right hand to understand the coordinates:

The units are Meters. If you do not define a width, height or depth, A-Frame uses the standard size of 1. The position is always in the middle of the primitive or entity.

<!-- Box with Zero position -->
<a-box
   id="box"
   position="0 0 0"
   color="#4CC3D9"
></a-box>