How do i find the dimensions of three different rectangles with the area of 6 cm^2

The area of a rectangle is (length) times (width).
So you have to find a pair of numbers that multiply to produce 6 .

If you only stick to whole numbers, then I don't think there are three
different ones.  You're going to need one pair that multiply to 6 and
are not both whole numbers.

After I explain how to solve problems, I hate to give answers.  But with
all due respect, I have a feeling that I haven't nudged you enough yet
for you to use my explanation to find the answers on your own.
So here are some answers:

1 and 6
2 and 3

and sets of dimensions that are not both whole numbers, like

0.6 and 10
1.2 and 5
1.25 and 4.8
1.5 and 4
2.4 and 2.5