How does rank reset/placements work? (Sil 1) and will i be send back to b5?

Im just asking since i still dont really understand how it all works

When rank resets i know you do placement matches but before then i was always in bronze Wondering now that im in S1 where will they put me after the place matches?

kinda worried because last time i remember i was in B1 promos then before i finished them i got put into placement matches. After those i was sent back to B5. Will that or something like that happen again?