Your business, be it in goods or services, has to be recognised in the marketplace. A registrable trademark, which can be one or more words, a device, or some other sign, is a means of achieving and maintaining that recognition and protecting the goodwill of your business. Registration of a trademark provides an enforceable right to exclude others from using that trademark or very similar trademarks.
Trademark searching before use is essential, as the effects of having to rebrand can be devastating to your business.