A full node is a copy of the Malairte software that downloads the entire blockchain, validates every block and transaction against the consensus rules, and relays valid data to other nodes. Running one is how you participate in the network without trusting anyone else to tell you what is true.
A node is not a miner. Mining produces new blocks and earns MLRT; a node verifies blocks and keeps the network honest and decentralised. Importantly, the Malairte node software holds no wallet and stores no keys - it validates the chain, it does not sign transactions or custody coins.
To run one you need a always-on computer, modest disk space, and a steady internet connection. The node downloads the chain from genesis, checks it independently, and then stays in sync at the chain tip.