Ideally, when we make an illustration we should be careful to create each object in order: first those that should be lower and then those that should be higher, but it is very rare that it can be so. So we have a very useful option which is to order.
In the example we show here, the blue object is below the brown one. If we want it to rise above we have to go to the "Object" Menu and then to the options "Raise, Lower, Bring to the front, Lower to the bottom". In this case we can indicate "Raise" and the blue square will be placed above the brown:
"Raise" and "Lower" raises objects step by step or level to level, while "Bring to Front" and "Lower to Bottom" raise or lower the object above or below all available objects. Of course, I remember that this option works within each layer. Therefore, an object on a lower layer will never appear on top of one on a higher layer.