If you have started to use the warehouse management capabilities of AX2012 R3 then one of the jobs you will get to is label printing. There maybe different types of labels you might print based on how you package and handle your items. The item numbering as it relates to barcode and important concept to understand. There are also different strategies and software options for printing labels.
If you are starting to explorer options for printing with WMS, these blogs offer some good background reading.
Kurt has a great blog post on labeling concepts.
These two posts from Ivan are a good background on setting up labels to use with the WMS functionality.
This is the AX documentation page on some of the print settings as it relates to different areas of the WMS setup.