How would I change the offset of a TextLabel in a script?

I need to change the offset of a textlabel for a GUI that I'm working on. I want the offset to be 100. Here's the current script I have.

script.Parent.Size.X.Offset = 100 -- script.Parent is a textlabel

This doesn't do anything though, even if I add a while true do loop. So, how would I format this correctly so that the X offset actually changes?

P.S. I have no idea how people figure these types of things out. I mean, how did people find out Vector3? It just seems like a big mystery.