Find a tutorial on how to use the Pen tool to make paths (make sure you do change the pen tool to 'paths' though, from shape layers/fill pixels) - that way, with a bit of time, you can precisely cut things out - once you've made the path and completed it (back to the start and 'sealed' path) you click on the 'paths' tab on the right (next to layers and channels) - there you'll see the path you've made. CTRL+Click the path and you'll see your path 'selected' - with it selected, hit CTRL+J (this will paste your selection onto a layer of its own (check the layers tab, you'll see it). Alternatively, with the path selected, you can (make sure you're on the right layer) hit CTRL+SHIFT+I - this will select the inverse (the background around your car) - now you can hit CTRL+SHIFT+U to desaturate it (black and white) - this will make the background black and white and leave the car ncie and colourful... or you can play with other stuff once it's selected. There will be videos around on how to use the pen tool properly, it's a bit fiddly to start with but it's great once you get it.
Sorry can't give much more advice, quite busy at the moment...