In my opinion, first step should be to get four basic documents.
First one you should get is the short version of the datasheet for your microcontroller. It shouldn't be more than 20-30 pages, so do read it whole before touching the microcontroller. Don't panic if you don't understand everything (or anything!). Just read it a couple of times. While reading it, there are few thing you should pay attention to. The page you'll probably use the most is the pin configurations page. It will probably be one of the first pages. It may be a good idea to print it and keep it close to the microcontroller. There you'll find out what each pin does.
After that, it would be a good idea to get the whole datasheet. It will probably have several hundred pages, but you don't need to read it whole at once. Instead just read the bookmarks list and if you're having any problems with a specific feature, read the part of datasheet which describes it. It would be a good idea to take a look at electrical characteristics page. There you'll find relationship between voltages and frequencies, voltages for high and low, maximum output currents and other important information without which your microcontroller can die. That part may just be few pages long, so do read it.
Next two documents are a bit more complicated, but they focus on some things that are very important. They are Atmel AVR042: AVR Hardware Design Considerations and AVR040: EMC Design Considerations. They're a bit scary at first, but do read them, since they're only around 17-18 pages each. In them you'll find ways how to correctly connect the reset pin, what types of decoupling capacitors to use (you didn't mention these on your parts list for example), how to set them up and so on. As with other manuals, you don't have to worry if you don't understand everything at first. Since you're a beginner, just focus on parts which explain how to connect reset pin and how to use decoupling capacitors. For the rest, it's good read, because at one point your microcontroller board probably won't work and you'll need to figure out why. You'll be able to find some pitfalls there.
I made an AVR board few months ago and had some beginner questions about it. For example how to connect decoupling capacitors when pins aren't close.
Also take a look here. Similar situation, except that guy had ATmega 16. I wrote a bit about setting up the toolchain and getting a programmer there.
Best Answer
PA0will be defined as 0 so the following line:Equates to shifting 1 left by zero bits, leaving an OR with the value 1 to set the first bit. Whereas the following line:
Is doing an OR with zero so won't change the registers at all.