When you view a Label from Zubi it will be set to the default sizing.
This default sizing may not work for you, e.g. all the text may not fit on the label. The red parts in the size indicators and on the label show the label needs to be adjusted to ensure it all fits.
You can change the label size; margins to which the data will print; the size of the main font or header font. Once the text fits, the red warning indicators will disappear.
Keep adjusting the numbers in the label format screen until you get a sizing that works for you.
Once you have a label that works you can save the settings for that specific label. The next time you open this label it will have the same size setting and you can print without needing to adjust each time.
To learn about printing labels created by Zubi see here.