retrieving information from a shape file loaded in ArcMap.

[shasam]

Hi,

Newbie to arc objects programming and using c#.net.

I have loaded a shape file in ArcMap.

I need to programatically edit(change the value) of  an attributes field called inVehicle to 50 from the shape file.

1) How do I reference to current loaded shape file?
2) how do I retrieve the attribute field called inVehicle and change its value?

Some code snippets would be of great help.

Thanks