If you've ever studied the piano, one of the things that you do to learn the instrument is to study scales, where you learn a certain fingering on the piano, and you move up and down the piano, and certain notes, and it changes the positioning of your fingers and so on. Well, scales to the piano are the same as rudiments to the drum.
There are a certain amount of exercises that you want to go through to increase the productivity of what you do with your hands. Up to this day there are 40 standard current rudiment on the Percussive Art Society list, and the basic idea of rudiments would be to start with some rolls, and then move into some hand combinations and different sticking combinations.
You might have heard terms like flams, and paradiddles, and diddles, and drags, and ratamacues, and those are all part of the exercises of rudiments, and rudiments can apply to your hands, it can be applied to your feet, they can be split apart between hands and feet to create alternate exercises, they could be infused in grooves, they can be infused in different exercises around the drums to get your body more mobile around the drums.
There are many uses of rudiments, but the best place to start is on a snare drum, or a single drum, or a pad, to start working your hands, to get your coordination going with exercises, sticking combinations, and the list of rudiments.