This bit of code will help you if you need to extract a certain text or data from a particular string.
The main thing to note here, is that the Extract option will only save the results into a Collection variable, even if you know you're only getting one result back. So you should be aware of this when extracting data. Although when you look at complex regular expressions, they look daunting, they actually aren't. You just need to spend a little time playing around with them and maybe running through some tutorials and you'll be well on your way to build awesome business solutions.
Nintex Workflow 2010
Nintex Workflow 2013
SharePoint Server 2010
SharePoint Server 2013
If you want to learn more, take a look at this site, which is one that I go to often to if I need a refresher - RegExr: Learn, Build, & Test RegEx
I hope this explains a little on how to use Regular Expressions in your Nintex Workflows. If you have any questions, please free to post them in the comments section.