What is Bitcoin core?
It's a free open source software which connects to Bitcoin network as a full node. It's synchronize all payments which happened in the Bitcoin network. You can use this software as a wallet of bitcoin. It's secure wallet and its created by satoshi Nakamoto who is invented Bitcoin. Through this wallet you can send Bitcoin to someone and receive Bitcoin from someone. But you can't buy and sell Bitcoin. For trading Bitcoin you should visit some cryptocurrency exchange. Here you can find more information about Bitcoin core
Sourcehttps://en.m.wikipedia.org/wiki/Bitcoin_Core