First lets execute shell script, later we will talk about execution permissitions
my file is file.sh which is on Desktop of current user
Open your terminal
If your current directory is not Desktop
check it by trying this command
this prints current working directory
chmod 744 file.sh
if this is not working then try
sudo chmod 744 file.sh
what is this 744?
this is the file permission
7 : 4 : 4
1 1 1 : 1 0 0 : 1 0 0
R W E R W E R W E
Owner of file : Group of Owner : Other
R: Read Permission
W Write Permission
E : Execute Permission
You can set this permission as per your need and wish.
this has included for the sake of file security.