There are 2 ways to locate latitude/longitude positions on your plots. The status bar displays the current latitude/longitude position of the mouse. You can also the Locate Position menu item button to place a marker at an exact latitude/longitude position on the current plot. For the latter, you will be presented with a dialog requesting the latitude and longitude values (default is center of plot). A marker will appear at this position. You can turn this positioning marker off by re-clicking the menu item/button. Note that if the latitude/longitude position is off the current plot, the marker will not show on your plot, but if you move the map area to one which contains that position, the marker will appear.
NOTE: With either method, the latitude/longitude units will be either decimal degrees or degrees, minutes, seconds, depending on how you have set the latitude/longitude location units. You can set the units (decimal degrees or degrees,minutes,seconds) for locating positions on your map. Simply right click on the map and choose the units you want.