putting it simply reading a file allows to read say a document; write permissions allow you to write i.e edit the document. But a document say something.txt is a text file an not a program. IN windows you have .exe which are "executable programs" .
So the "execute" permissions are to do with running a program.
So lets take a simple example.
lets write a mini bash script.
echo hello world
save the above two lines as helloworld to Desktop
if i go to go to desktop
//note captial letter
and type ls -l i get :
-rw-r--r-- 1 andrew users 30 Jan 18 13:50 helloworld
it shows because i'm logged into my linux as "user" and i created a file i have default permissions; these are read write but not execute if i try to "run" this script i get permission denied .
if i am on Desktop i can run it as follows:
to give me execute permissions i do :
chmod 755 helloworld. Nopw when i run it it outputs " hello world"
Thanks Capitaine, I will have a little practice of that when i get home.