After launching the ATEM Software Controller, click on the Media tab at the bottom of the screen. 

The ATEM can have up to 20 graphics loaded into the system.

Navigate to your graphics from within the ATEM, or drag and drop them from an open Finder window.  

Now that you have loaded all the graphics into the ATEM, you need to load your first two graphics into the Media Players. Just drag and drop them into each of the Media Players in the panel on the right side of the window.

Note:  You can only have two graphics set up to key at the same time.  If you have more than two graphics for the show you will need to change out the ones loaded into the Media Players as needed.  

Once all graphics are loaded and set up in the Media Players, click on Switcher to go back to the video switcher and set up the downstream keys. 

Now click on the Palettes tab on the right side of the ATEM Switcher.  Then click on the Downstream Keys tab from the list of options.  

There are two Downstream Keys - Key 1 and Key 2. 

You need to set the FILL SOURCE as the Media Players.

For Key 1 - Set the FILL SOURCE to Media Player 1

For Key 2 - Set the FILL SOURCE to Media Player 2

Next,  UNCHECK the Pre Multiplied Key button.

You should not have to adjust the settings under Clip: and Gain:

These settings adjust the transparency of the .png file

Repeat these steps for Key 2. 

You now have your graphics set up in the Media Players and these graphics are now ready to be keyed over the video.  

On the right side of the ATEM window are the two Downstream Keys. They are labeled as DSK 1 and DSK 2.  

DSK 1 will key the graphic that is loaded into Media Player 1 and DSK 2 will key the graphic that is loaded into Media Player 2.

When ready to show the graphic on screen you can click the ON AIR button.  The graphic will stay on screen until you the click the ON AIR button again. 

The ON AIR button will cut the graphic on and off screen.   The AUTO button will fade the graphic on and off screen. 

NOTE: Usually for a graphic such as a lower third you should keep the graphic on screen for about 3-6 seconds.  Usually a good rule-of-thumb for editors is to read the information on the graphic twice before pulling it off screen. 

To change the graphics that are currently loaded in the Media Players you need to click on the Media button at the bottom of the screen. 

The current files that are loaded into the Media Players are indicated by the small numbered (1 or 2) icon on the top left of the graphic preview.  These are indicated by the highlighted yellow squares.  

To change a graphic, just drag the desired graphic to the Media Player window on the right side panel.  Repeat this step for Media Player 2.