The Creative settings control the settings for the Creative as a whole.
Here you can control the Animation, Border, Responsive behaviour and Weight optimization for your Creative.

Besides the Creative settings there are also the Element settings. with special settings for Elements like Video and Effects.
To access those settings click on a specific element and select the tab "Settings".

Set the duration of the timeline.
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At the end of the defined time all animation (including repeat and autoplay video) will be stopped in order to comply with IAB standards.
Only user-initiated animation and video will continue.

By default all animation will be stopped at the end of the duration.
Select "Continue" and animation (including repeat and autoplay video) will continue indefinately.

Turn on "Show Border" to draw a border around the canvas of your Creative.
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You can use this to make sure your Creative complies with IAB standards for Creatives with a white or black background.

To enable Responsive behaviour in your Creative go to the Settings and set "Enable" to "on".
Now the behaviour is turned on for all Elements in the Creative.

Find the full Responsive documentation here.

In the header the "Estimated weight" is being displayed.
This is showing the current overall size of the Creative.

To reduce the final weight you can set the maximum JPEG Quality and "Target Pixel Ratio".

Find the full Weight optimization documentation here.