Printing addresses onto postcards in done in one of three ways:
VDP: Variable data printing by using a spreadsheet to input addresses onto the postcards inline.
Inkjet: A post-process that is used to apply addresses in sequence to finished products. This process is a specialty service and fairly expensive though sometimes worth it.
Labels: The DIY method, printing labels is the least efficient way to apply addresses to cards.
All these techniques rely on well organized spreadsheets.  As long as you have that, we can print your addresses right onto your postcards.