Hardwood stores sell a small implement called a "stud finder" but you can also just tap on the wall in a line till you hit a stud. It will feel solid. If your house is not antique chances are the studs are 16" apart.
You can pick up a stud finder from any hardware store. They are often very affordable.
See if these help you.
Stud finder is inexpensive and easy to use. You run it across the wall and it will show depth changes.