In algebra, letters are used to represent unknown numbers, and numbers are used to represent known values. The letters and numbers are used together to create equations that describe relationships between the unknown and known values.

Think of it like a puzzle. In the puzzle, you have some pieces with numbers on them, and some pieces with letters on them. The pieces with letters represent the unknown pieces that you need to find. You use the pieces with numbers to help you find the unknown pieces.

For example, if you have the equation "x + 2 = 6", the letter "x" represents an unknown number, and the numbers "2" and "6" represent known values. The equation says that if you add the unknown number "x" to 2, you will get 6. To find out what "x" is, you can solve the equation by subtracting 2 from both sides. This will give you the answer "x = 4".

So, in algebra, letters and numbers are used together to represent unknown and known values, and to create equations that describe relationships between the values. It's like solving a puzzle, where you use the letters and numbers to find the missing pieces.