To participate in governance, Curve Finance users need to lock their CRV into a voting escrow.
You can do so at this address: https://dao.curve.fi/locker
veCRV stands for voting escrow CRV. They are your CRV locked for voting. The longer you lock your CRV for, the more voting power you have (and the bigger boost you can reach). You can vote lock 1,000 CRV for a year to have a 250 veCRV weight.
Your veCRV weight gradually decreases as your escrowed tokens approach their lock expiry. A graph illustrating the decrease can be found at this address: https://dao.curve.fi/locker
You can only vote using your voting weight at the block where a proposal was created.
Simply visit the proposal of your choice, click your vote option and confirm your transaction. You can find DAO proposals at this address: https://dao.curve.fi/dao
You can visit the Curve Finance governance forum at this address http://gov.curve.fi/