Welcome to Android Central! What do you mean by the main screen and a free space? Are you talking about one icon showing up in the App Drawer (i.e., the All Apps list that shows up when you tap the icon that looks like a grid of dots), and the other showing up on the homescreen?
It's normal for the icon to show up in your App Drawer, because that's what shows you all apps that are installed on your phone. There's a setting in the Play Store ("Add Icon to Homescreen") that will automatically add a shortcut to your homescreen. I usually turn this off, since I like to control what appears on my homescreens.