How to install certain modules only for specific site using Acquia Desktop I am using Acquia Desktop for creating multisites.
Problem is whenever I am installing a module it gets replicated in everyother site.
What i need to know is that if i want to have a module only for specific site do i need to first manually create a modules folder inside the site folder such as practice.localhost\modules (where practice.localhost is the site name) folder as the modules directory is not created by default for any of the subsite folder.? Is my approach correct 
Moreover I have also heard that if we create modules for specific sites then we are going to find it difficult to export sites to FTP for making the site go online.?
do i need to first manually create a modules folder inside the site folder such as practice.localhost\modules (where practice.localhost is the site name) folder as the modules directory is not created by default for any of the subsite folder.?


Yes, you need to create a specific modules folder for the specific site(s) you wish that module to be available for. If you want it available on, say, 10 out of 20 sites, you'll need a copy in each site's modules folder. You can remove the need for this by making it available in sites/default/modules, but obviously it will be available to all sites in the multisite.


  are going to find it difficult to export sites to FTP for making the site go online.?


Completely depends on your deployment process. You'll probably want to review that process before implementing this on your live servers, but whether or not it's 'difficult' depends on what you need to do.