What exactly do missionaries do?

Missionaries tell the Gospel to people that are in a different area of the world or have a different culture.

This isn't as easy as it may sound. First they have to raise support. Often taking as long as 3 to 5 years to get enough churches and individuals to meet their financial needs. Then they need to learn the language. They need to understand the culture, what's considered rude, what to do and not do so as not to be offensive. They need to establish a trust with the people they are ministering to and build long-lasting relationships. And they need to stay in contact with their mission agency and supporters on a regular basis.

Why go to all that trouble? Simply because they are deeply compelled by God to go and tell the good news.