The sine function is a wave about the x axis, starting at zero, the origin, and rising to 1 then dropping back through zero, dipping below to -1, then rising again to cut the axis and continue undulating like this indefinitely. It also undulates when x is negative in a similar way, starting from the origin and dipping below first. That much you probably already know. Sin2x is a particular case, but the cycle period changes from 2(pi) to (pi) so the frequency is doubled, twice as many undulations. I think you know that, too. One complete cycle of sinx is between two values of x separated by a value of 2(pi); while the separation for sin2x is (pi). The intersections for sinx are n(pi) where n is a positive or negative integer including zero; those for sin2x are n(pi)/2. So there's no conflict.
If y=2sinx, the period is the same but the amplitude is doubled, so the intercepts are the same as sinx but the height and depth of the wave (peak and trough) are different, ranging between 2 and -2 instead of 1 and -1. For y=2sin2x the amplitude and frequency are both doubled (that is, the period is halved, because frequency=1/period).