How to change file/folder permissions in linux

Recently i crossed through a serious issue of folder permissions.. I installed xampp in /opt folder which is under file system.. And i was not able to add or copy files into that folder. Even in the properties bar the option is shaded as i was not logged on as the root user.. Now, its the time to know how to unlock all permissions.
User permissions can be provided using the command “chmod”. We have to specify for which user we are going to give permission and what permission we are going to approve.
u user/owner
g group
o other
a all
and file permissions are
r read
w write
x execute
what to do?
+ add permission
- remove permission
= set exactly this permission
For example,
$ chmod a+rwx /opt/lampp -R
In the above example i gave permission to all the users for read, write and execute inside lampp folder under /opt. If you add -R the permissions will also get applied for the subfolders. For more details use manual
$ man chmod
Once you finish above tasks we need to solve the phpmyadmin error..  First we have to change permission for my.cnf file. Type this command
$ chmod 644 /opt/lampp/etc/my.cnf
and then open /opt/lampp/phpmyadmin/libraries/Config.class.php . Search for
$this->checkPermissions();
replace with
//$this->checkPermissions();
save the document and restart xampp .