In the first Holmes story, A Study in Scarlet (published 1887), Watson, as the narrator, describes meeting Holmes, their subsequent sharing of rooms at 221B Baker Street, his attempts to discover the profession of his taciturn companion, Holmes's eventual taking of Watson into his confidence, and the events surrounding their first case together. Watson describes Holmes and his methods in detail, but to Holmes's taste, in too romantic and sentimental a manner.
In some of the stories, Watson attempts to solve crimes on his own, using Holmes's methods, with limited success. Later, in films, this approach is taken to further extremes -- Watson is often portrayed as a sputtering bumbler. In Conan Doyle's own stories, however, Watson is clearly a capable and brilliant individual -- simply, however, not endowed with Holmes's skills and almost superhuman ability to focus on the essential details of the case. Watson's intelligence serves as a foil to Holmes's own. In modern terms, Watson is a searchlight whereas Holmes is a laser: both brilliant, both useful for their purposes, and both remarkably different in their function.