What is a mission?

I just pulled this from Wikipedia because they got it perfectly right:

"Missionaries of The Church of Jesus Christ of Latter-day Saints (LDS Church)—widely known as Mormon missionaries—are volunteer representatives of the LDS Church who engage variously in proselytizing, church service, humanitarian aid, and community service. Mormon missionaries may serve on a full- or part-time basis depending on the assignment, and are organized geographically into missions. The mission assignment could be to any one of the 405 missions organized worldwide.
The LDS Church is one of the most active modern practitioners of missionary work, reporting that it had over 75,000 full-time missionaries worldwide in August 2013[1] (as well as over 22,000 part-time church-service missionaries at the end of 2012).[2] Most full-time Mormon missionaries are single young men and women in their late teens and early twenties and older couples no longer with children in the home. Missionaries are often assigned to serve far from their homes, including in other countries. Many missionaries learn a new language at a missionary training center as part of their assignment. Missions typically last two years for males, 18 months for females, and 6 to 18 months for older couples. The LDS Church strongly encourages, but does not require, missionary service for young men. All Mormon missionaries serve voluntarily and do not receive a salary for their work; they typically finance missions themselves or with assistance from family or other church members. Many Latter-day Saints save money during their teenage years to cover their mission expenses."

I will be serving a mission in Federal Way, Washington State. It's English speaking, so I don't have to learn a new language. I've been saving money since I was in elementary school and started getting an allowance, so that I could pay for it myself.