One thing..If you've never used layers and masks you might want to try accessing the "Quick mask" feature. It's a good way to get comfortable using basic masking techniques. For a beginner...using layers and masks can get a bit confusing...just saying..when i was a beginner i learned to order my processes and use only selections and Quick mask, when i needed it.
There are tons of things you can accomplish without the use of layers and layer masks. Learn to feather your selections properly and to use "Quick Mask" in order to get started. I did the version of your picture above using no layers/layer masks...just selections with Lasso tool properly feathered for each area and a tiny bit of quick mask (not great, and has flaws that should be fixed, but, a useful exercise in very basic selections...took less than 5 minutes).
Once you're comfy using Quick mask you'll be much more comfy using the masking system in Layers. Those guys up there are correct..layers and masking is very powerful, much can be done, MUCH....And, for a beginner, perhaps, much to much. It can get confusing if you get all Layer crazy with a bunch of masks and if you don't understand how the ordering affects things.
Quck mask...Make a conventional selection using something like the "Lasso" tool..watch the "ants" form..
Press the Q key and you'll see a bunch of red on the screen, that's your mask..the red stuff. (it's red because there is an old history behind red masks in photography..You can change this color if it moves you to REVOLUTION!)
Hit the "B" key to get the Brush tool > select a feathered/soft edged brush for starters, adjust as required and play with opacity in the tool control center for the Brush tool...set the foreground color to black and you'll paint Red..black=red=mask, nothing will be affected undenrneath red. Set the foreground color to White and you can remove Red. The open areas are the areas that will be affected by your process. RE: the combo of opacity and feathering of the brush will come to you..it takes time to learn by DOING.
When you have finsished painting on your Quick mask Hit Q again and it takes you back to "marching ants"... Excecute the process you wanted the mask for...
Hope that was useful