When the 'X, Y' function is selected (Shortcut ) as shown here Draft it will select the next point using X & Y values of the current Units. These co-ordinates are measured as relative values from the previous point. If there is no previous position such as when defining the first point on a line then the values are measured from the drawing origin (X0, Y0) and no dynamic dimensions are displayed.
The X co-ordinate value is in the left hand box with the Y co-ordinate value in the right hand box. As you move the cursor the values are updated to reflect the values of the dynamic dimensions, simply click the left mouse button to accept the current screen position and therefore the values displayed.
Alternatively you can type in the values. Click in either the X or Y text field and you can edit the value as required (double click in the field to select the whole current value which can then be deleted or over typed as required). As soon as you type in either field Draft it will lock the field and cursor movement will be locked in that axis. You must click the button to unlock if you wish to release the value. To accept the values typed into one or both boxes click the mouse when the cursor is within the drawing area. Both values are unlocked automatically as soon as the point is accepted.