If there's no air resistance (virtually always the case), range is simply horizontal velocity * flight time.
Two things to keep in mind.
1. Since there's no air resistance, Vox=Vfx in other words there's no acceleration in x direction so that velocity is constant throughout flight. (here, I'm only talking about freefall motion).
2. Flight time is determined by vertical velocity and NOT horizontal velocity. The equation u use depends on the nature of flight. Is the obj launched from ground and follows a parabolic path or is it launch horizontally from a cliff etc etc.. Flight Time is 2*(Vy/acceleration) for a parabolic flight (ground-->max height-->ground) otherwise, depending on the variables u have, use one of the kinematics equations with a time variable.
I think it's much better to conceptually understand what the variables/terms represent and their inter-relationships than memorizing when to use what kinematic eq..
But again, range = horizontal velocity * flight time.. horizontal velocity is almost always pretty easy to find, Eq for flight time depends on the nature/symmetry of the flight, worst case scenario, use kinematic Eqs..
