Evaluate the function at the specified values.?

I have 4 problems but I'll only ask two (believing that two will be enough of an example)

the first is

f(x) = {2x+1, x<0

{2x+2, x (greater than or equal to) 0

with

a. f(-1)

b. f(0)

c. f(2)

the second seems a bit more confusing (especially since I don't even get the first one .... hehe)

f(x) = {3x-1, x (less than or equal to) -1

{4, -1 (less than or equal to) x (less than or equal to) 1

{x squared, x > 2

with

a. f(-2)

b. f(-1/2)

c. f(3)

I dont know really what these problems are asking; am I to plug in each of the a,b, and c (tho at different times) to see which equation is true and then into the greater than/less than? do i each part seperately????? I just really need examples of how someone does this and maybe an explanation?

Thank you for your time!