There is a lot more to basic mathematics - too much to list here, but there are plenty of textbooks and online resources available.

HCF stands for Highest Common Factor, whereas GCD stands for Greatest Common Divisor, but they refer to the same thing. The HCF (or GCD) of 24, 60 and 96 is 12.

LCD stands for Lowest Common Denominator. You might also come across LCM (Least Common Multiple) as an alternative. The LCD (or LCM) of 24, 60 and 90 is 360.

That probably depends on local conventions. I've never come across "composite factors" and prefer the term "divisor" when I intend it to mean a factor that's a positive integer. Thus, I could assert that a composite positive integer is the product of positive integer powers of its prime divisors.