As somebody who's recently had cause to instruct a lawyer about Trademarks, I now know a little bit more about it that I did.
Essentially, you pick what you want to trademark. Logo, phrase, company name etc, and at least one category.
The category list is (from memory, it was a few weeks ago) about 50 strong. Contains things such as Veterinary care. Medical. Transport. Computing/IT. Food. Alcohol. Holidays. Tourism - that sort of thing. It's designed to cover every aspect of business, and inevitably is somewhat vague and overlapping at times.
There is a cost to this, albiet a relatively small one (low hundreds), and a smaller per-category cost for each one you choose from the list.
The idea is logical, in that you mark those where your company does or may operate in to protect your name and reputation.