It's quite common that you want to add a new Drupal module to your site. And Drupal has made this process very easily. But due to lack of the knowledge of Drupal folder structures, the module is installed in the wrong way, which increase the future maintenance cost of your site. In below, we will talk about how to install drupal module properly.
Download Drupal Module Source Code
In order to install a module, you will need to download the source code, and unzip it. The best place to find the 3rd party module is in Drupal official site: http://drupal.org/project/Modules, there are huge list of free and useful modules you can use to setup a powerful web site.
Upload Drupal Module Source code to Proper Directory
Then, we come to the most important step - unload the code to the correct directory. What the "correct directory" here means?
Drupal can recognize the new module if you upload the source code to one of the below directories:
-{Drupal}/modules/
-{Drupal}/sites/all/modules
-{Drupal}/sites/{site}/modules
And each of above directory has its own purpose.
As a best practice in using open source project, it would be good to keep all the customized code to one place and don't touch all the core code the open source projects have developed. This will greatly reduce your maintenance cost when upgrading your code to next version. For Drupal, the centralized directory for customized code is {Drupal}/sites.
For directory {Drupal}/modules/, this is the place to place the Drupal core file, even you can install your module there, we would like recommend you not to do it.
And for {Durpal}/sites/, if you want this module can be used by all the sites you host in your Drupal instance, it would be good to place the module source code to {Drupal}/sites/all/modules. And the module installed in {Drupal}/sites/{site}/modules will be only available in the specific site.
Active Drupal Module
You can go Administrator->Site Building->Modules, check the the module you just install and save the configuration to active it.
Now, you should be able to use the new module now.
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