The first step, to add, subtract, or compare fractions, is always to convert the fractions to equivalent fractions, that all have the same denominator. You can use one of several techniques to get the LEAST common denominator, or simply multiply the two denominators to get a common denominator (which in this case may, or may not, be the smallest common denominator).
To compare two fractions, find a common denominator (multiplying the two denominators will always give you a common denominator), convert both fractions to the common denominator, then compare. Another - actually easier - way to compare two fractions is to convert both to decimal. Just pick up a calculator, and divide the numerator by the denominator.
its always going to be in the denominator of 2 fractions.
Fractions will always equal 1 when their numerator is the same as their denominator
a common denominator
Not always. If one denominator is a multiple of the other, the LCD will be the larger one.
That their sum is always equal to the denominator.
Both proper and improper fractions have a numerator and a denominator. In a proper fraction the numerator is always less than the denominator. In an improper function the numerator is greater than the denominator
Only if you have just two fractions.
Its probably easier if you see percentage as a fraction (always with a denominator of 100) this puts it in the same area as other commonly used fractions such as one half, one quarter etc.