Downloaded and installed bitcoind--bandwidth usage gone through the roof
Bitcoin Core is full node software. This means that it will download, validate, and keep up with every transaction made in Bitcoin's history and future. Its goal is independence: if you run a node, you know that everything you see adds up (no theft, no money created out of nothing, ...), without relying on anyway else's judgement. However, it comes at the cost of high resources.

This is one of the ways of interacting with bitcoin-the-currency, but certainly not the only one. A good resource for finding wallet software is here: https://bitcoin.org/en/choose-your-wallet