Roman Numerals are symbols that stand for numbers. All Roman Numerals are written using some different symbols, either by its self or together. These few symbols are I (1), V (5), X (10), L (50), C (100), D (500), and M (1,000).
Roman Numerals are written from left side to right side, using the rule of addition in most causes. A person first writes the 1,000s, then the 100s, then the 10s, and then the units. To write 2,763 you would write MMDCCLXIII. So basically all you do is add the numbers together to get a longer word.