how does reposting work

when I repost something, it obviously goes into the "reposts" section on my account

when it shows up on someone else's FYP, it says I've reposted it

however, does me reposting it just label the video that I've reposted it, or does reposting make it more likely the video will appear on my friends' FYP.

is it a guarantee it'll go on their FYP? Does it make the chances higher it'll end up on their FYP?