Seeding is used to match up players in such a way that the best players do not play and knock each other out super early. So just take a simple example of a local tourney with 16 players. You rank the players based on skill from 1-16. Very talented players will get seed 1-8 while the newest (and worst) players will get seeds 9-16. Then in the first round of bracket, seed 1 (super good player) plays seed 16 (super bad player). 2 plays 15, 3 plays 14, etc. TOs (tournament organizers) rarely actually rank each individual player. Instead, they rank by approximate skill, and then let the tournament program (Tio, usually) randomly set up the bracket. So if you have 4 players who are all really good and equal in skill, they will all be ranked the same and Tio will randomly select which one plays the lowest seed. This works the same from the bottom, so when you attend your first tournament you will likely be the last seed along with a few other players who are also new.
If this sounds unfair that you have to play really good players first round, just keep in mind that the alternative is that the good players have to play each other first round. Not only would Mango vs. Armada in the first round be extremely unhype, but it would make the loser's bracket super lame because either one would most likely work their way back and completely mess up the expectations of other players. If I happen to get Mango in my half of the loser's bracket, it's unfair for me compared to someone on the other side who doesn't have a player of equal skill. That means someone could get ranked higher than me solely because Mango and Armada were seeded poorly.
This is all for the standard double elimination bracket. For Apex, if you decide to enter, you'll be participating in pools. Pools are seeded the same as bracket (8 players, with each player ranked 1-8). The point of pools is to get more accurate seedings for players that the TO couldn't possibly know the skill of. So if the pool has top 4 advancing to bracket and you are 5th seed, you can still get that 4th place spot to advance by beating the 4th seed (or another seed, but the 4th seed is the one you're most likely to upset). Another benefit of pools is that you will be guaranteed at least as many matches as there are players in your pool. Instead of losing to two really good players in a row and being done, you will get to play a good number of players of all varying skill levels. Hopefully you get the gist of how seeds work based on this. There's a lot of extra info you can find on seedings, pools, and other tournament formats (Swiss, single-elimination, etc).
