A spacing class has two parts: what and how much.

p is padding and m is margin; add x for both sides, y for top and bottom, or t or b for the top or the bottom alone
the number counts steps of --spacing, which is 0.25rem (4px at the browser's default text size): 1 is 4px, 4 is 16px, 6 is 24px and 8 is 32px

Any step works, even p-13 or p-1.5, and p-px is exactly one pixel. A minus in front makes a negative margin: -mt-2. Spacing on just the left or just the right waits for the right-to-left lesson, because there is a better way than left and right.

Space is a scale