This is using an older version of Photoshop, but the tips in the video are still relevant.

• What am I clicking on? (or: why double-clicking on a layer seems to do something different every time)
• Create a new layer
• Move & select layers
• Transform layers
• Group layers
• Duplicate layers
• Duplicate layer effects
• Merge layers
• Fill layers with a colour
• Lock layers
• Layer opacity
• Layer blend modes