A node runs the Bitcoin Core software (or another reference implementation) that allows users to interact with and participate in network consensus by maintaining a copy of the Bitcoin blockchain and validating transactions and blocks.
Note while all miners are nodes, not all nodes mine bitcoin. Importantly, running your own node gives you a vote in consensus as it independently validates blocks and transactions according to Bitcoin's protocol rules. This means it can reject blocks or transactions that do not comply, contributing to the democratic decision-making process within the network.
An example of node runners attempting to enact an update or change to the Bitcoin network was during the 2017 'Blocksize Wars,' where node runners supported a User-Activated Soft Fork (UASF). Users proposed new block size rules independently of miners, effectively voting and influencing the network toward accepting the protocol change.
In addition to participating in the governance of the Bitcoin network, running your own Bitcoin node provides a user with increased security as you are not dependent on a third party as well as privacy since you can connect to the network anonymously.
Users can download the open-source Bitcoin Core software on its official GitHub repository.