I really need help with pi?

You simply need to memorize the following formulae...

A = π * Radius * Radius or πR^2
C = π * Diameter or πD

Remember that the Radius = 1/2 the diameter
Now, just multiply...

A = 3.14 * (2cm)^2 = 3.14 * 4cm^2 = 12.56 cm^2
C = 3.14 * 4cm = 12.56 cm

Note that the answers seem to be the same, but one is in Square centimeters, and the other in centimeters. Area and Length are different.

1)
a = πr^2
(area = pi * radius * radius)

π(4/2)^2
= 3.14(2)^2
= 3.14(4)
= 12.56 cm²

= = = = = = = =

2)
c = πd
(circumference = pi * diameter)

4π
= 4(3.14)
= 12.56 cm

C = pi*d
C = pi*4
C = 4pi cm

A = pi*(d^2)/4
A = pi*(4^2)/4
A = 16pi/4
A = 4pi cm^2

Area = pi r^2
circumference = 2 pi r

where
r= radius = d/2
d= diameter
pi approx = 3.14 (by your assignment)

Area = (3.14)(2)^2 = (3.14)(4) cm^2
you can multiply this out.
circumference = (2)(3.14)(2) = (3.14)(4) cm

You do the rest. (If you have been discussing
the topic of "significant figures" then you might be only able
to save the result to the nearest ones place)

The equation is:

C = dπ

You're given the diameter and the value of π to use, so just plug them in and solve:

C = 4 * 3.14
C = 12.56 cm