How Does Seeding Work In Tennis?

Seeding is a type of elimination method to ensure that a player of high skill strength does not confront each other in the early rounds. There is no requirement that a tournament have seeding although most elimination type competitions do. The tournament committee shall determine the seeding.  Basically in seeding it has the higher ranking players against the lower ranking players so that the higher players will play against each other later to make the competition more interesting. Seeding is directly related to skill ranking. For most tournaments it is worldwide ranking that gets them seeded. In some tournaments (like Wimbledon) follow a different way to seed participants. In these tournaments they are seeded as to their performance in the same tournaments the year before, and a player's grass court expertise to seed the top 16 men and 16 women.

Seeding is a system used to separate the top players in a draw so that they will not meet in the early rounds of the tournament. The top seed is the player  the tournament deems the strongest player, they and the second seed are placed at opposite ends of the draw so if they both continue winning they will meet in the final round. The number of seeds is based upon the size of the draw...

So why was Serena ranked lower than the other girl, who never won ever

They use a magic 8 ball