Let’s say there are five candidates - A, B , C, D, and E.
Let’s assume candidates A & B are the most popular.
Personally I choose to rank them as C, E, D, B and then A.
Out of all of them, no one gets over 50% of the #1 vote. Whoever gets the lowest #1 vote is knocked out first. Let’s suggest that this is C. All of their #1 votes and therefore my vote is then transferred to E.
Let’s suggest that after this there’s still no one who has over 50% of the vote between the other four candidates. Let’s further assume that candidate E has the lowest resulting vote after the first round of knockout. My vote is then transferred to candidate D.
Out of A, B, and D, let’s assume none of them still have over 50% of the vote after this redistribution. Let’s further assume that D has the lowest vote of the three. My vote is then transferred to B.
Given there are only two candidates left, one will have to have a majority. That candidate wins.
Under RCV, as long as you mark every box with a preference your vote can never ever be wasted. It will always end up with a candidate that wins or one that loses, but it cannot ever be exhausted and therefore meaningless.