most of the process running you can quickly lookup on the web or you can bring up the system documentation for them ...
for example on mine I have a couple process running
to bring up more information about an app running you can usually type 'man <app-name>'. for example 'man sshd' will bring up information about the SSH server that is running.
as for executable that is determined by file permissions... not by file extension. if you execute 'ls -l' to get a detailed directory listing on the left of the files you will see a string of characters similiar to this:
rwxr-xr-x root users ... etc
This means that root is the owner of the file, users is the group of the file. As such the first three letters (rwx) mean that the owner has read, write, and execute permissions. The second group (r-x) means that members of the file's group have read and execute permissions and the third group (r-x) means that everyone has read and execute permissions. the 'x' or executable permission is what makes a file executable.
in a nutshell