Lin and diego are discussing two expressions x^2 and 2^x

The expression a^b

means that we multiplicate the number a by itself b times.

So x^2 means that we multiplicate the number x by itself 2 times:

x^2 = x*x

and 2^x means that we multiplicate the number 2 by itself x times

2^x = 2*2*2 * ... * 2 (if you count them, you should see x times the number 2)

for example, if x = 4, we will have

2^4 = 2*2*2*2