@IAmAPerson Hexadecimal is just a different way of representing numbers. Our regular number system goes:

1, 2, 3, 4, 5, 6, 7, 8, 9, 10.... 99, 100... 999, 1000

Notice that we increase the number of digits on the tenth number (then 100th, then 1000th); this is because we use the decimal system, or base 10. This means that each digit can represent an extra power of 10 values, so 1 digit can represent 10^1 values, 2 digits can represent 10^2, etc. Hexadecimal is base 16, so we don't increase the number of digits until we reach the 16th number. This means that each hex digit can represent an extra power of 16 values, so 1 digit can represent 16^1 values, 2 digits can represet 16^2 or 256, etc. This means we need to "make up" some digits:

1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F, 10.... FF, 100.... FFF, 1000

In this case, A has the decimal value 10, B has the decimal value 11, etc. 10 in hexadecimal has the value 16 in decimal. 100 has the value 256.

I didn't really explain it well, so here's the Wikipedia page (which may actually be more confusing): http://en.wikipedia.org/wiki/Hexadecimal

In Petit Computer, the HEX command will just take a decimal value (say 17) and convert it into a hexadecimal string (which is &H11; the &H signifies that the number should be interpreted as 11 in hex, not 11 in decimal). Hexadecimal is particularly useful in computer programming (and thus Petit Computer) because each digit of hex can represent 4 bits. Hey, you know what else is 4 bits? The information that makes up sprites! Remember, a sprite pixel can only contain one of 16 colors, so each pixel can be represented by 4 bits. This is why you use HEX to represent the data in a sprite... it's just easier that way. Also, 2 hex digits can represent a full byte, which can take on the values of 0-255 (which is also useful).