There are a lot of resources for putting together a wiki.
There are a couple of free platforms:
and Plone are very flexible and free. However, it probably requires an IT person to get it set up.
There are also several web-based platforms that anyone can start by just signing up. Most of them will give you a site for free, as long as you keep the whole thing public. If you want to make it private, you have to pay them a fairly small amount of money.