It is very easy for you to participate. If you are familiar with Wiki editing then start by writing a whole new lesson or contribute to the already existing ones through discussions in the respective lesson's discussion page.Check out the Content Development page here.
For those who are new to WikiEducator, check out the WikiEducator tutorials here for your self study. You can also enroll in the ongoing Learn4Content Free Online WikiEducator Training Sessions. You might find it relevant to also subscribe to the Learn4Content Discussion Forum here.