If you are wanting to assign barcodes and/or QR codes to your Assets or Catalogue Details, this is a relatively straightforward process. The barcode field in Assets is in the Extended Tab, and the barcode field Catalogue is in Stores> Catalogue, in the Details tab (instead of the Extended tab. where the barcode is assigned in Assets). The Catalogue barcode can be generated into a QR code on the Catalogue>Details Tab:
Catalogue Barcode Assigned and QR Code Generated from Details tab
Asset Barcode Assigned in Extended Tab
The Asset barcode field is in the Extended tab, however the QR Code can be generated back in the Details tab:
Asset QR Code Assigned in Details Tab
There must be a barcode number for scanning and for generating QR Codes. A list of all your barcodes and QR Codes if you want to generate these too) can be found in Reports, where they can be printed on stickers or as a printed reference to attach to catalogue items and/or assets.
Some more info for you here: Barcoding in MEX and FleetMEX.