Citations are crucial for local SEO so if you want to rank for local keywords and in the Google Maps results then you need to have good citations as well as good on-page local SEO and a good Google My Business profile. So for the on-page SEO I suggest that you include your NAP (Business name, address and phone number) well throughout your web site and also include schema which includes those details, then obviously include location details in your content and meta data.
So these citations are business listings on UK business directories that include your NAP details, so they provide a link and also help your local SEO more as they contain that NAP.
My citations are of a very high quality though and much better than most provide, I ensure that each citation has unique and high quality content which means that they all get indexed. Most citations don’t get indexed so this makes them a much higher class of citation and very effective at boosting your local rankings.