Take a flock of birds - would be great to make them look like they are literally flying above your layout? No problem!
1) Get you background sorted - create a new fill layer or open an existing texture.
2) Now copy and paste your birds into a new layer (pasting in will automatically add them into a new layer for you)
3) Get into the habit of labelling your layers (in the drop down list called "layer properties")
this will save you ages later on if you end up with lots and lots of layers, trust me!
4) Now select the bird layer and create a drop shadow.You can do this by going to your styles pallette (if not open, go to the Window menu at the top and click on Styles). Select the grey square button that (when hovvering over it) says Basic Drop shadow. You will notice that the birds instantly gain a shadow and look like they are floating a bit. If you look at your layers palette you can double click the layer effects button on the right of the layer name and a drop down list of all the effects you have applied appears - you can switch them on and off by clicking the eye (just like you switch on and off layers). If you double click the style, you will get a pop up window with options. Try playing with the drop shadow options and see what happens. You can create a deeper shadow with wider spread to make them look higher up or even change the default dark grey shadow colour to any colour you wish!
5) Once you understand how simple drop shadows work, try putting different birds into individual layers and giving each a different shadow effect and different heights. It can look fantastic if you scale each bird a tiny bit to match the height (slightly bigger the higher up they are etc).
Hopefully this has given a little insight into just one of the many effects you can apply to layers in a way that is very useful for digital LOs. I am still learning my way round photoshop myself (despite using it for years - always something new to learn!) but am very happy to help or answer any questions as best I can - just ask away :)