Open cart is the free e-commerce script, so you may install and use for free. But there are default theme where are no face book like options. If you want to add facebook like or share option you need to create facebook like or share module, if you are a web developer you may create module using there developer instruction. Otherwise you need to free download or purchase module from OpenCart market.
Once if you have downloaded the facebook module follow the following directions.
1. Firstly, unzip or extract the downloaded archive.
2. Upload the file/folder in root directory; for example, upload the facebook.php file public html> admin> controller> Module.
3. Once complete upload all file properly you need to login your opencart website as administrator. If logged in then log out and login again.
4. Go to the Module option under Extensions and install facebook module.
5. After installation, click the Edit button, there are iFrame codes required. To get the iFrame code visit its facebook developer link and create facebook custom like buttom entering you facebook page URL Example”http://www.facebook.com/oscbdcom”,
6. Push Get code a put up windows will appear and select from the top “IFRAME” and copy the code.
7. Paste the code in required box and setup place where you want to show the like button and save it. And see its work properly.