quick question on ARM + ldr

What exactly is happening here?

ldr a1, [v1], #4

Is it loading the number 4 into the contents of v1 and loading that word into a1?

If not then what is it?

a1 = [v1] 
v1 = v1 + 4

ARM is a lovely architecture. You'll realize as much as soon as you learn about the adr macro instruction.