this is the error message i got when i tried to install extension from my computer. i don,t know what to do

JFolder::create: Could not create directory
Unable to write entry

This means that there are some server settings which are wrong. You have to go to your global configuration and click on server. The first field is Path to Temp-folder and that's most likely the local path of you local install. You have to give in your live server path.
There are multiple ways to find that path. The easy one is to create a path.php file that has the following code in it:
<?php
echo getcwd();
?>
Go to example.com/path.php and this will give you the right directory. Put /tmp behind it, place it in Path to Temp-folder and your done.
When you do not use FTP your directory and file permissions need to be set. The problem is that there are a lot of directories and their default setting is 755 which is safe and makes it impossible for users of the same server to place files in you directory. 755 does not make it possible to install or uninstall languages, templates or extensions.
If you change it to 777, you will be able to install and uninstall all your stuff, but… its not that safe.
To make it easy you can make a php file which sets all the directory settings right to 777 when you want to install stuff, and sets it back to 755 when you are done.