Howdy and Welcome to MFK!
Since you posted this question in the planted section, I assume you have a planted tank. Generally, it is not always advisable to use air stones in a planted tank with demanding plant species, since it drives out the CO2 from solution. Although you may not have a CO2 system, this might reduce the baseline CO2 in your tank. Furthermore, there might not be a need for aeration, depending on your filtration, the fish you keep, the amount of plants and the size of your tank.
Assuming you just like the looks: There is no limit as to where you put an air stone. You can even cover it with some gravel and hide the tubing this way. I personally like it best if the viewer cannot see where the air comes from, i.e. hide it behind a rock .
Have fun trying things out,
HarleyK
ps
In case you don't have one, yet: Get a valve to hook up along the tubing between your pump and the aquarium. It prevent backflow and, thus, draining and/or damage if the pump stops.