A bit fuller description of what it is about:
Long ago, the Seven Days of Fire, a war/cataclysm occurred. Humanity released the God Warriors and they destroyed nearly everything. Most of the world is dominated by poisonous fungal forest inhabited by bizarre insects, with desert dominating most of the rest of things. There are many small countries, each scheming against the others. Nausicaa is the princess of the Valley of the Winds. She loves animals, is expert with her glider, and is willing to risk her life for her people. Late one night, a huge Tolumekia plane crashes in the Valley of the Winds with something in its cargo hold...
An important thing to add, though, is that there are two editions (at least) of this anime around in the United States. One is a fansub which lets the original through rather well. The other, which was the official release, was The Warriors Of The Wind. It is a hideous dub job, which rips the storyline to shreds. That release was the reason that Miyazaki didn't want anyone to touch a translation of Princess Mononoke until Neil Gaiman convinced him that he would do the Right Thing with it.
Also note that this story is available as a much longer and slightly different manga.
Finally, the soundtrack on this anime is excellent, particularly the Interchange with the Ohmu theme.