There are two common tools used to specify attitude. First and quite common one being [https://en.wikipedia.org/wiki/Euler_angles Euler angles]. Basically, you start with an initial frame and tell by what angle and about which axes you need to do the rotation. Repeat this two more times each time using the ‘newly’ obtained axes post rotation. The final frame achieved is your required frame.This set of three angles are specified in the same order. Euler angles tells you how to get from one frame to another and hence the attitude. <br \>

The second method is to use [https://en.wikipedia.org/wiki/Quaternion quaternions]. Any arbitrary rotation can be entirely done about a unique axis and using a particular rotation angle about it. So we have four parameters in a quaternion; three to give this axis as a vector (vector part) and one for the rotation angle(scalar part). These four are intertwined in the sense that the vector part doesn’t give you the axis alone.<br \>