Hello BB201,
I have added the power wires to your layout diagram. I have made it very simple and suitable for a new starter. When you gain more experience you can add additional isolated sections but they are not necessary to start with.
Your layout is basically an inner loop and an outer loop with a branchline from each loop to a terminus station. The inner and outer loops must be electrically separated with insulated joiners.(isolators)
You will require at least two power packs to operate this layout and this will allow you to have two trains running at the same time. I am assuming that the loops cover a large area because you have shown three separate stations on them. Because of this I have attached power wires to four points around the loops to allow for voltage reductions caused by resistance in the wiring. They might not all be required.
I am also assuming that you are going to use "thinking" or "power routing" turnouts such as the Fleischmann ones as with these you do not need to have insulated joiners and separate power wires for each of your sidings. The turnouts will control the power reaching the sidings.
I hope this helps you.
BB210_layout01.jpg