Hey Martha, mainly there are 2 types of ExpectedConditions which can be used with Explicit Waits:
ExpectedCondition < WebElement > : This is the type of condition which has a web element locator as parameter. The wait applies the condition which tries finding the web element, depending on its status. If the condition can find the element, it returns the element as result, otherwise the wait tries the condition again after a short delay.
For eg. elementToBeClickable(web_element) or elementToBeSelected(web_element)
ExpectedCondition < Boolean > : This type of condition has a string parameter. The wait applies the condition to the parameter. If the result of applying the condition is true, true is returned as result, otherwise the wait tries the condition again after a short delay.
For eg. titleContains(String title) or urlContains(String url)