You have 2 options available in the viewport to control the placement of new strokes.
Hint : Hover your cursor over a setting to see more information about it.
You can choose to place the drawing plane on the World Origin at $(0, 0, 0)$, on the 3D cursor, a 3D mesh surface or another stroke.
You can Choose a plane orthogonal to the view, on the global XY, global YZ, or global XY plane or on the local XY plane of the 3D cursor.
By default the 3D cursor is not visible in the 3D viewport in 2D Animation. Enable it in the overlays :
To move or rotate the 3D cursor, you have to open the "N" panel with N, and go to View > 3D Cursor Panel. You can also change the tool in the left hand side and move it with the mouse in Object mode.