In order to vote on the given proposal, you need to have a sufficient amount of tokens at the time when the block was created. This means that if you attempt to vote on a proposal and block number is in the past, and you were not holding the required token yet, your vote will not be counted.
Go to your project's snapshot.page
Click on “Connect wallet” button in top right corner
Connect with wallet provider where you hold relevant token
Click on the option you want to vote for
Sign the message via your wallet and done