Now a days we are used to have interfaces that effortlessly adapt to different kind of devices. Advertisements are not the exception: we want ads to be able to run on all kind of environments and devices. Achieving this, on the other hand, is not something that happens automatically.
To start with, just in case, we recommend to double check and confirm that you are in need of a cross-device creation. Even though cross-device is common, sometimes unclear information can lead to unnecessary extra hours of work trying to cover multiple device layouts.
This is definitely an approach we encourage, but before you get started, open the template you received (ifs o) and check its structure. Many templates have a divided structure where we indicate a content holder (an HTML tag that serves as wrapper) per type of device or per general size. These are either desktop, tablet and smartphone, or, large, medium and small.
We have used this approach for many templates because we noticed that responsive or liquid layouts where causing issues and delays for many ad builders.
If you need to work with one of these templates, simply fill each content holder as usual but make sure you test them using emulators and on the actual devices they will run on.
If the switching-holders approach does not suit you, because for example you want to use CSS responsive content, make use of the shared holder if available or contact support through email@example.com to see what the best way is to avoid possible issues.