It’s admittedly confusing, since there are different ways to clock (drive) an MCU, and we’re sometimes guilty of loosely (and incorrectly) referring to all of them as “crystals”. A true crystal has two leads, and requires external capacitors to get it to vibrate. But there are also 3-lead parts called resonators (see the related products below), which are like crystals with built-in capacitors (this may be what Ben was using). There are also oscillators, which take power and ground and produce a square wave at a given frequency. To complicate things you can find all of these in multilead packages, which can make identification difficult. And finally the ATmega (and many other MCUs) has the ability to use internal clock sources – no external parts necessary! The ATmega datasheet is a long one, but it has a good section on clock options and how to set up the chip for them. As Toni says do take a look at the Redboard kit, as the schematic is pretty foolproof. Good luck and have fun!
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