A balloon filled with helium will rise because of its density, which is the ratio of the mass and volume. The density of a helium filled balloon is less than the density of the surrounding air, which...
The amount of helium in a tank depends on how big the tank is (volume), the pressure of the helium and its temperature. It is calculated from the ideal gas equation with allowance for compressibility.
When you look at atoms at that small of a level, between them you actually have empty space- nothing at all like in space. Even between the nucleus and its electrons of an atom itself there is a lot...
You have to first obtain a helium tank and then affix the balloon to the nozzle of the tank and turn on the valve, releasing the compressed helium into the container ie. Balloon. But do not leave the...