The red marker shows your currently selected location. You can change the location by either;

1. Searching for a place name.
2. Enter your what3words address
3. Dragging the marker or clicking on a new location on the map.
4. Entering your coordinates and time zone manually.

Enter place to search for
Search results

Use the mouse to drag the map, and if you have a mouse wheel, you can use it to zoom in and out, otherwise, use the controls in the top left corner of the map to zoom and scroll.