Picking planes and locations well is very important in X-Plane, for obvious reasons.
To open an aircraft, go to: File / Open Aircraft. You will then see the contents of your Aircraft folder, inside the X-System folder on your hard drive. Select the category of aircraft you want, and then select the aircraft. You will then see the contents of your aircraft's folder, which contains the paint and .acf file. You will see a file with a picture of an aircraft on it: this is the aircraft. Click it, and bingo, you're done.
Handy Tip: If you download an aircraft from the Internet, make sure you place it inside the Aircraft folder in the X-System folder. This is because X-Plane will not open anything outside of your X-System folder.
To place an aircraft at an airport, click on 'Location' in the menu bar. Then click 'Place Aircraft By Airport', and a window will appear with all the airports listed in it. At the bottom of this window are to text areas. One of these is long, and is located on the left, and the other is short, located on the right. The short one is for entering the ICAO code of the airport, the long one for the airport's name. You only have to fill in one of these.
Let's say we want to place our aircraft at Sydney International, in Australia. In the big text area, we can type 'Sydney', and all the airports beginning with Sydney will appear automatically. You can then find 'Sydney Intl'. Press the 'Place Aircraft by Airport' button, and you're there.
Alternatively, you can enter the ICAO code. Instead of typing in 'Sydney', just type in 'YSSY'. Sydney Intl will then be highlighted.