The basic purpose of the Timeline is to control movements of your objects in 3D space. The Timeline isn't the one really moving your objects in 3D space. Rather, the Timeline gives you insight as to when what will be where in the 3D space.

Without the Timeline, it will difficult, if not impossible, to time our animations. The timelines helps us to know the number of frame or frames we are on, and how many more frame(s) are left, and so on.

First of all, by default (in Blender's default layout arrangement), the Timeline lies at the bottom of the screen. It looks like this image. The green vertical line you see is the pointer.
It tells us the frame on which we are.
There are two ways to read the frame on which we are on. The first is to look at where the point is and plot downwards to read the value on the x-axis of the timeline.
And the other, the simpler way, is to read the value from the little box beside the play and stop navigation buttons.

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