Click the Apple button in the upper left corner and choose 'About this Mac.'
If you are running OS X Mavericks or earlier, click on 'More Info'. Otherwise skip to step 3.'
Here you will find details about your Macbook, including the screen size, processor type, and model year.
Click 'System Report' for additional specifications such as model identifier. Click 'Storage' to find hard drive capacity (round up to the closest option.)