|Only integer numbers can be represented as hex AFAIK|
Conversion: The value of a IEEE-754 number is computed as:
sign * 2exponent * mantissa
The sign is stored in bit 32. The exponent can be computed from bits 24-31 by subtracting 127. The mantissa (also known as significand or fraction) is stored in bits 1-23. An invisible leading bit (i.e. it is not actually stored) with value 1.0 is placed in front, then bit 23 has a value of 1/2, bit 22 has value 1/4 etc. As a result, the mantissa has a value between 1.0 and 2. If the exponent reaches -127 (binary 00000000), the leading 1 is no longer used to enable gradual underflow.
Rounding errors: Not every decimal number can be expressed exactly as a floating point number. This can be seen when entering "0.1" and examining its binary representation which is either slightly smaller or larger, depending on the last bit.
Other representations: The hex representation is just the integer value of the bitstring printed as hex. Don't confuse this with true hexadecimal floating point values in the style of 0xab.12ef.