Firewall is a software or hardware device that protects your computer from being attacked over the internet by hackers, viruses, and worms. This may occur either at a large corporate network, or simply at a small home network; both have the same security issues.

A Content Delivery Network (CDN) is a system of the network that deliver pages and other Web content to a user, based on the geographic locations of the user, the origin of the webpage and the content delivery server.
In other words, CDN is generally used to take in web content from others webpage based on the geographic locations of that user to the origin user webpage.

A SSL Certificate stands for Secure Socket Layer. It validates your website's identity, and encrypt the information visitors send to, or receive from, your site. This keeps thieves from spying while exchanging of information between the sender and receiver. When your website is protected by SSL Certificate, the visitor can assure that this website is trusted/secured to make any transactions or exchange an informations.