Can I still use my oven, even if it has melted aluminum foil stuck to the bottom?
I doubt you have melted aluminum foil at the bottom of your oven.  The melting temperature of aluminum foil is 660 degrees Celsius (1,220 degrees Fahrenheit) at standard pressure.  It is possible that you have a layer of grease between some foil and your oven bottom.  This combination will likely char and burn.  I would clean your oven well, and use as normal.