On this screen you can trade and edit each team's (pro & minor league) roster & lineup however you like. Any changes will be used for Exhibition and Pennant (season) games. You can also use players that you purchased in the VIP Shop, they will appear in the "FREE" box.
Right side of screen: The baseball diamond shows you how many players there are at each position. This only represents "natural position", so even though you may have only 1 "true" first basemen, you will definitely find other players on your team who is capable of playing 1B as a secondary/sub position.
The numbers in the red box tell you how many right & left handed pitchers you have along with total pitchers. So it shows there are 27 RH, 9 LH and 36 total pitchers. In the green box it shows batters. There are 14 RH, 15 LH and 1 switch hitter for a total of 30 batters. At bottom it notes there are 3 foreign players and 66 total men on the roster out of 70 max.