"so if I enter = x = 5
and then go to the next cell and enter
I would expect the answer to be 25. Instead the answer is x^2."
Are you putting an = in front of your x=5? If so I think you might have gotten a warning message. You don't need an = in front of those.
Are you, assuming you are using Microsoft Windows, holding down the shift key and then pressing enter while your cursor is sitting at the end of x=5
If you do that do you see it display a second line showing just 5? (Well actually there are In:= and Out= in front of those, but do you see the 5?)
I am assuming you are missing the shift enter step.
Read this and see if it helps.
If there are still problems then reply and we will see if we can figure it out and get you started.