If your church is trying to reach the mission field, if you really want to reach new people to introduce them to Jesus Christ, the main audience for your website is people who are checking out your church. If that is the main audience, the main purpose is giving them useful information and insight into your church. This doesn't mean that you can't have other things on your website. It doesn't mean that it can't have some other purposes and functions. It just means that the main purpose, the lens through which you will evaluate how functional it is, is "how well does it reach out to people who are checking out your church online?"
Here are some things visitors will need to see:
An obvious place for new visitors to click - If someone is getting to know your church for the first time through the website they shouldn't have to wander around looking for what they need to know.
Worship time and location - It should appear in several places on your website. If someone is wondering whether or not to come to your church to worship, they really need to know when and where to go.
What you believe - People investigating your church want to have a general sense of what you believe. Are you a snake-handling church. Do you believe in Jesus?
What to expect - if you want people to come to worship it helps to tell them what they can expect when they get there.
How to contact you - Your website may catch the interest of a first-time visitor. But what if they want to know more? Help them get in touch with you via phone, email and even text message, twitter or even plain old postal mail.
Pictures - On the web, a picture is worth more than a 1000 words. Fortunately, with digital photography, this is cheap and simple. Find someone at your church who is a decent photographer and makes sure you have photos. Photos of your building and worship space are fine, but more importantly, show your people and show them being the church.
There is a lot more you can do with your website. If you start with these things, you will be well on your way to having a website that will reach out to new people who are searching - searching the web and searching for God.