There's more to buying a tripod than fitting the screw to the camera. The screw part is easy. There are only 2 sizes, 3/8" and 1/4". 3/8" is used for fitting to heads and some medium format cameras. The rest (majority) are using 1/4" and this is probably what your (most) camera has.
The hard part is to find one that fits 1)your budget, 2)the weight consideration and 3)the weight it can comfortably hold.
So firstly, you will need to know what kind of weight you are going place on the tripod, if it's able to hold the weight steadily. Many people have tried to save on tripod but it becomes costly when the tripod topples with your equipment on top.