Training is easy, you have to start by hiring a coach by betting on one and hope that your bet is the highest. You can bet for one coach per day. In order to use coaches on players you need to go to your players tab and select which coach you wanna use on which player. Remember you have 10 units per day for each player so you have to figure out a best ratio between team tanked, soloq and training that works for you. Now the coaches will start increasing the certain skills of players and this is important when playing against other teams because higher skills means higher winning chances.
Let me know if there are any further questions.