(But if you want to dive in and learn: Bitcoin Core is the original open source software project that is "Bitcoin." Bitcoin Knots is a modification of Core that has different mempool (new transaction queue) policy, because there is disagreement about what the mempool policy should be. The most critical part of the software, the consensus code, is the same between the two. This mempool debate has long-term ramifications and it's connected to many other debates about the software, but it's nothing for nubees to be concerned about.)