I am new in Window Mobile Programming. I have to make to scan Wifi networks and join to the network using Window Mobile 6.5 Professional device, CE OS 5.2. But I do not know how to start it.
Please give me tips to start it. What language and tool is better? Where is the helpful documents?
You will need Visual Studio and the Windows Mobile SDK. As for languages, I recommend C++. You can use C#, but for the project you described, you will end up invoking the native C functions anyway.
The functions you need are in the Zero Config API.
A good resource for beginning Windows Mobile programming is the 30 days of windows mobile series.