intecel

I'm new to weightlifting. Two days ago I worked on my arms on the machines at the gym. Yesterday and today my left arm won't completely extend without being in a bit of pain.

Is this normal when starting out? Should I possibly have taken it a little easier on myself?

My right arm is sore, but I can extend it, and I am right handed so I really do more with my right arm than my left normally.

A friend of mine says that this is normal, and it lets you know that you're muscles are building. I could understand that being true on my right arm, but my left is a lot weaker and pretty sore when I try to move it around.