Bitcoin cash is a another alt coin based on a change to the original bitcoin network that allowed changes/improvements in its software to create a faster, and more secure way to transfer digital cash. A big change to the network was allowing an increased block size limit. One of the most restrictive parameters of the original bitcoin is blocks are limited to 1Mb in size. Bitcoin cash block size limit default limit is 8Mb, and can be adjusted in the future if need to accommodate extra demand on the network.
Before the bitcoin cash blockchain was launched a snap shot was taken of the original block chain, so everyone who had bitcoin at the time of the snap shot would be credited with the same amount of bitcoin cash on the new bitcoin cash blockchain. Learn more here