Hi Bo,
The download circuit is shown in many places, particularly Manual 1, for example pages 27 and 44. Unfortunately, a supply decoupling capacitor is not shown, although one is included on all the project boards. For a simple circuit, the value is not too critical (10uF and/or 100nF are typical), connected across, and close to, the supply/ground pins, Legs 1 (+ve) and 8 (-ve). It's mentioned many times on the forum!
Typical input switch circuits are shown in Manual 3, particularly around Page 26. For unused inputs it is recommended to pull the pins low OR high (it doesn't matter which). The internal "Weak Pullup" resistors (about 35 kohms) are quite a new feature so are not well documented in the manuals, but explained in the PULLUP command in Manual 2 (~page 159).
Sorry, I don't think there is any single overall circuit diagram shown in the manuals, because there are just too many different possibilities. But there are often examples on the forum.
Cheers, Alan.