How do you check one box in a GUI.SelectionGrid?

I am currently working on an inventory system. It it working pretty good and recognizes what I am collecting. I have now moved on to actually using the item. My theory was, when a box in the inventory is selected, a comparison is made. Unity will try to see if the texture in the box matches any texture in a master list of textures. If it matches wood then it must be wood {do something lol}. My problem is, I can’t figure out how to check one box when using GUI.SelectionGrid. Unity keeps trying to check every box, so it will tell me that box 4 has wood (when it doesn’t) because I have wood somewhere else in the inventory. Please Help!!

The SelectionGrid function returns the index of the selected element.

So if you pass it an array like this:
{wood, stone, water, gold}

a return of 0 means wood is selected, 3 means gold, etc.

int selection = GUI.SelectionGrid(.......);
if(selection == 0)
{
  //You have selected wood
}
//or
switch(selection)
{
case 0:
  //wood
  break;
case 1:
  //stone
  breal;
//...........
}