Question

the set of symbols in the roman numeration system

Answer 1

As used today:
I = 1
V = 5
X = 10
L = 50
C = 100
D = 500
M = 1000

Some authorities suggest that over-scoring is use to multiply a symbol by 1000, but there just are not enough examples to say this is a rule rather than an improvisation used by some individuals.

When a less numeral comes first, it is deducted from the following numeral

IV = 5 - 1 = 4
IX = 10 -1 = 9

However this is not always done, so
4 = IV = IIII

Answer 2

This year in roman numerals: MMXIV

My age in roman numerals LXV

1957 in roman numerals MCMVII