A tune with a time signature of 4/4 (also known as "common time") means that there are four beats in every bar, and a quarter note gets each beat. Thus, the upper number indicates the number of beats, and the lower number designates which note value gets each beat. Some 4/4 marches are simple and straightforward to play, but others can seem daunting with their complexity.
In this class we learn Murdo's Wedding. This tune is super easy because there are only 4 truly different bars in the tune. Once you've learn all 4 you just need to make small changes and put them in a different order to get 2 parts of a tune!