Two settings decide what lands on the board: which reaction counts, and how many of it a message needs.
The star emoji is the reaction the bot counts. Members add it to a message they think is board worthy. You can keep the classic star or use any custom emoji from your server. Pick one that is easy to recognise and is not already used for something else, so counts stay meaningful.
The threshold is how many of that reaction a message needs before it is reposted. Set it too low and everyday messages flood the board. Set it too high and nothing ever qualifies.
You can decide whether the author's own reaction counts toward the total. Leaving self stars off keeps the board honest, so a post has to earn stars from other people, not from its author.