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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 \>
[[File:Euler1.gif|thumb|center|400px800px| Any target orientation can be reached, starting from a known reference orientation, using a specific sequence of intrinsic rotations, whose magnitudes are the Euler angles of the target orientation. This example uses the z-x-z sequence. GIF reproduced from [https://en.wikipedia.org/wiki/Euler_angles#/media/File:Euler2a.gif here]]]
In the above gif, we are trying to reach to a final orientation of the globe. However, the order of axis about which these rotations are done are predefined (here, z-x-z) and this in turn fixes the euler angles. But the problem with euler angles, as you may have noticed,is that these angles are not very intuitive. The axes of rotation and their order are decided beforehand. Now, how do we decide the angles constraining ourselves to that specific order? Not easy, is it? <br \>
[[File:Quaternion1.png|thumb| Quaternion plaque on Brougham (Broom) Bridge, Dublin. Image reproduced from [https://en.wikipedia.org/wiki/History_of_quaternions#/media/File:William_Rowan_Hamilton_Plaque_-_geograph.org.uk_-_347941.jpg here]]]