While creating a lesson you can 'lock' one or more elements on a slide. Locked elements cannot be moved or modified until they are unlocked.
To lock one or more elements on a slide, follow these steps:
Click an element you'd like to lock in place
Click the options button (⋯) in the top-left corner
Click Lock
To unlock an element, click once more on the lock icon.
💡Tip: To select multiple elements, either drag a selection area over them or click one element, hold Shift, and click the others.