A player is either you or the soccer players. This page is about the Soccer Players. There are two ways to get a player. One is your first team, and the other is by signing one in the "transfers" menu.
The best way to get more players is to transfer them. You can get Free Transfers (which are usually players with low stats or players that you've released), or you can pay for players in the general transfers section. These players are normally better, although there are some exceptions. The price on these players can scale from 10 coins to about 900 coins.
There is one option on the menu that says Player Development. Once you click it, you can train your players which will make their stats higher and make them better overall. For more information, click here: Player Development.