To start using Bitcoin you will need to connect to the Bitcoin Network. Bitcoin Classic is a so called "Full Node" and it builds the backbone of the network. It offers high levels of security, privacy and stability. However it has fewer end-user features and takes a lot of disk-space.
Bitcoin Classic is the best portal to the Bitcoin network with various features that allow you to use Bitcoin to the fullest.
To get started, you need to install the software and after installation the client will start downloading the entire blockchain of historical data (some 120GB at this moment). This may take half a day to several days, depending on how powerful your hardware is.