What's the difference between General and Weekly Availability?

General Availability is your general time slots to conduct lessons on each day of the week. In contrast, a Weekly Schedule allows for a specific time of a particular week where you could add or remove time slots, perhaps when you are busy with work or studies.

Both availability calendars have green cells corresponding to those time slots that are available for the teacher to teach and white and grayed-out slots corresponding to those time slots that are blocked. 

To set the slots to "available", just click on the first time slot and drag the mouse cursor down to the last slot. The teacher can create multiple blocks of time that they are going to be available for each day.

Please make sure you're not just clicking on one slot, because that would only create a 15-min block.