Placing shapes in front of another

To place one shape into another on the same shape layer or something else?

If you want to add shape to existing on the same shape layer then hold down Shift while drawing shape. 

To subtract shape from existing on the same layer hold down Alt while drawing second shape.

To intersect shape from already drawn shape on the same layer hold down Shift + Alt while drwing second shape.

You can combine additional paths into a shape layer. Shape  layer are fill layer. That have a empty fill, or a solid color fill, or  a gradient fill, or Patten fill.  You can also add a vector layer mask to a pixel layer like a combined layer.  You can also stack shape layers to had different fills.

When you use one shape to conatain another they call it a 'clipping mask' which is good to know if you want to look it up or youtube it..... so you have a layer and another layer on top.... put your cursor in between the two layers and alt-click .... the top layer will now sit inside the bottom layer ( or right-click the top layer and select "create clipping mask")