strip -s
 

I type strip -s on one of the program I installed and it gets smaller.

I read the man page and it says it removes symbols. What does that mean

Any functional difference between a program strip and before strip?

There are no functional differences in a program before and after stripping it. Basically what you're doing is removing symbols referring to functions and variables within the program that can be of aid when debugging using a debugger such as gdb (the exact nature of the symbols present in the executable will depend on how you compiled the program).