I am not sure about number two, but I can 'explain' (by explain, I mean link) to you number one:
Dale Ray can explain better
, but here's the general gist of it:
chmod is a Unix command for setting the permissions of a file. It is short for change mode.
Basically, it makes users able to read, write, and execute different things around the computer. It's largely helpful for making text files executable for frequently-used shell scripts.