He is in a relationship with Kelly Frears (Helen Hunt) and the two are hoping to get married, but Noland's busy job always tends to get in the way. As they are having Christmas with her family, Noland is called to make another trip and he must leave again.
On the flight, something appears to go wrong with the plane during a thunderstorm and Noland is the lone survivor. He washes up on an inhabited island with no way of contacting the outside world and call for help.
The rest of the film, for the most part, is Noland spending time on this island alone. As he's on the island, FedEx packages that the plane was carrying begin to wash up on shore and Noland collects them, and eventually opens them to find uses for them.
Of course, the best of those packages proves to be a volleyball that eventually becomes Noland's only friend on the island. In a strange way having Wilson was a way for Noland to stay sane (which is odd to say) as he was able to talk to him and bounce ideas off of him.
Noland ends up going from a man that had no true hunter/camping skills to an expert after spending around four years on the island.
I, of course, loved this film. When I first heard that Hanks would spend the entire movie on an island alone, I thought there was no way they could make that interesting. But, they totally did - and a lot of that has to do with Hanks' performance and the inclusion of a volleyball.
In fact, I feel the island portion of the film is far superior than the portion of the film where Hanks is interacting with the other humans. That is when the film seemed to get a bit more boring - which is odd.