...absolute

We can use the position property to set an element in a desired location in the page, by additionally specifying a horizontal and vertical position using the properties left, right, top, and bottom. These properties specify the distance (in pixels or some other units) from the (0,0) coordinates of some reference container. Usually, the reference container is the viewport (top-left corner of the browser viewing area).

...relative

To use position: relative, you need to know "relative to what?" Which element will act as (0,0) for this element? Set that element as position: absolute and then set your element as position: relative and set the coordinates.

...fixed

position: fixed is very similar to the absolute one, with the difference that the element remains in its position all the time, while the rest of the page scrolls up and down.