****NOTE: We have a NEW Online designer for projects started 10/18 with a BUILT IN help section. Click 'Online Designer Help' from inside the designer to access the latest info!***
Yes! You would add one layer for each size that you wish to use. You can also change what type of font for each layer.
Simply click the option to add text on the top left side of the online design template.
and then select your font and size (at the top of the design area).
Type into the field offered and drag and drop it to where ever you'd like to place it.