There are three types of permissions when using chmod:
Read - Read a file / List Files
Write - Write a file / Create, rename, and delete files
Execute - Execute a script
There are also the groups of users when using chmod:
Owner - The owner of the file
Group - The group to which the owner belongs
Other - Everyone else
Each of these three types of permissions is assigned a number. They are the following:
Read - 4
Write - 2
Execute - 1
The permissions are added down each column, like so:

Here are some example values:

If you are still having trouble here is a tool that may help you:
http://cmain.zymichost.com/CHMOD/
The Wikipedia page may also be helpful:
http://en.wikipedia.org/wiki/Chmod
How to Change File Permissions
The rest of this tutorial will take place in FileZilla which can be downloaded here: http://filezilla-project.org/
Step 1: Connect to your FTP using this tutorial: http://www.zymic.com/forum/Ftp-t59.html
Step 2: Right-Click on the file in which you would like to change the permissions of:

Step 3: Select File Attributes from the menu that appears:

Step 4: Change file permissions and click Ok:
