Como poner pantalla completa?

como puedo hacer para que no me aparescan los botones de abajo de la pantalla (atras,salir y pestanas)??

Hello Johan

Can't be done, at least not with App Inventor. Why though? If your App will be in the hands of Users, they are not going to be pleased if they can't control their phone.

Try the tools extension and it's HideSystemUI method, see also the test project there