Also referred to as the Oxford or Harvard comma, the serial comma appears before the final conjunction in a list of three or more things. For example:
In a moment of madness, my cat hopped onto the table and knocked off my keys, wallet, glasses, and phone.
But should you use it? Unlike some other grammatical issues, this one does not appear to be culturally based as either a British or American stylistic norm. It seems to be up to the individual or included as part of a university or college style guide. If you are currently studying, it might be a good idea to check your institute’s preference in this matter.
Personally, I use a serial comma only when sentences/lists are complex, such as:
It was only when I reached the futsal pitch that I realised that I had left my soccer boots, both shin- and kneepads, and also my socks at home!
Here, the reason for the final comma in the sentence is to ensure that ‘both shin- and kneepads’ are considered one item in the list. There is no right or wrong to this one. However, if you do use the serial comma, be sure to use it all the time, not sporadically, otherwise you will be called up for continuity issues!