This works because almost all the US uses first-past-the-post elections for the Presidential general election. So you get outcomes like this:
Scenario 1:
Biden: 10 votes
Trump: 9 votes
Kennedy/Stein/West: 0 votes
Biden wins the state
Scenario 2:
Biden: 9 votes
Trump: 9 votes
Kennedy/Stein/West: 1 vote
Tied vote, decided by game of chance/lawsuit
Scenario 3:
Biden: 8 votes
Trump: 9 votes
Kennedy/Stein/West: 2 votes
Trump wins the state
This is why you see huge financial support from Republican billionaires for third party candidates who have no chance of winning.
That doesn’t just mean “think about voting” either — it means checking your registration to make sure it hasn’t been purged, talking to people you know about how you’re voting and why, volunteering if you’re able, and financially supporting the campaign in an amount that’s within your budget