chmod

chmod is an abbreviation of change mode. There are two ways to chmod:

Symbolic (e.g. chmod +x)
Code:
chmod <people><+/-><permissions>
Example: chmod
o-w (deny others from editing the file)
Example: chmod
u+rwx (give the owner full control)
Exmaple: chmod
+rwx (give everyone full control)
Example: chmod
+x (allow anyone to execute the file)
Code:
Key:
r - Read
w - Write
x - Execute

u - The owner of the file
g - The group that the file belongs to
o - Anybody who is not one of the above
a - All users

+ - Add permissions
- - Remove
permissions

Numerical (e.g. chmod 700):
Code:
                    : The first octet represents permissions for the owner.
       r w x  T     : The second octet represents permissions for the group.
Owner:  4 2 1  7    : The third octet represents permissions for everyone else.
Group:  0 0 0  0    : For each octet, start at 0 and:
Other:  0 0 0  0    : +4 for read permission.
            : +2 for write permission.

Command: chmod
700         : +1 for execute permission.