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")
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.