Cutting a window to see your garage from within the house
You'd do this like you would add any other new window. Find the studs, choose a location, cut square holes in the drywall on both sides, cut sections out of the intervening studs to make room for the new window, and frame the new window properly like this:



Then you would flash the rough opening's sill with self-adhering membrane and install the window just like any other one, then repair the drywall on both sides and add trim.

However, in terms of the wisdom of this plan, it seems questionable for a variety of reasons:


It's probably a fire hazard; no window is going to contain a fire in the garage as well as thin sheets of rock (drywall), and this is especially true if the windows are framed in vinyl or wood.
Windows aren't completely airtight, so you're creating more routes for nasty gasses and fumes from the garage to enter the house.
The garage side of the window is going to continuously get dirty from car exhaust and need cleaning.
If you don't happen to own two fancy sports cars, or you use the garage for storage, the view may be less than stellar.
Anyone you try to sell the house to may be less than enthused by a window into their garage allowing them to gaze upon their dirty Toyota Camry and boxes of Christmas and Halloween decorations.