The layer at the top of the list is the one at the top of the stack (ie, the most visible of the lot). Layers have an "eye" icon, if the icon shows, the layer is visible. You can click the icon (or its absence) to toggle the visibility of the layer. Note that shift-click one such icons changes the status of all other layers, so shift-clicking by mistake can have surprising effects when you don't know.
Otherwise post a screenshot of your Layers list.
Otherwise post a screenshot of your Layers list.