The meanings will differ with context
numeral = a single written number like "1" or "4" not "23".
Eg Germans write the numerals 1 and 7 differently to the English.
The Roman numeral for 4 is IV.
MMXX is 2020 in Roman numerals.
number = a quantity, 0, 1, 45, 3E8, pi, -47,
Used for many things at different times.
Can be used to "numeral" or ""digit" sometimes.
eg pi is an irrational number
I can't read your writing. This number is twenty something? What's the second number/numeral/digit?
digit - usually a single character of a number.
eg The first digit of pi is 3. Clocks usually have four digits, for hours and minutes or six digits if they include seconds.
figure - Often used for digit. Sometimes used for number, but I suspect less often by a long way.
eg What's this figure here in this long number? I can't read your writing.
pi squared to two significant figures is 10.
"figure" and "figure out" are also verbs meaning something about working things out or your believe in something.
eg I figure it is too far to walk to town.
I can't figure this out.
Also means image, picture or course.