I would like to second Serenity's praise to Barbara Bennan. Her book is wonderful.
Keep in mind that the chakras aren't part of the physical body, but rather are part of the energy body. They are not bound by physical boundaries and do not match up exactly with any physical markers - the chakras are like energetic internal organs that have their own locations and subsystems connected to them.
The spine/front division of the five inner chakras doesn't make 12 chakras. Rather, consider them to be two sides to one chakra, or directional expressions if you rather.
The 'pole' running through the body doesn't exist as drawn. The central column is actually made up of two intertwined channels, one directed upwards and the other downwards. How they twist and where exactly they are forward/backwards is different for each individual but from my experience it is generally in the center of the body as Barbara Brennan describes.
Also keep in mind that the exact location of the chakras (forward/backwards, left/right, up/down) can all vary depending on the individual. In rare instances individuals have 'floating chakras' which can move around quite rapidly (making it hard to do a healing), or can even have two chakras swapped (only seen in once) or side by side (never seen it but heard about it).
The best way to find the chakras in your own body is through meditation. After you learn how to Ground and Center practice cycling energy through your body. Once you get competent at that, observe the cycling more passively. Once you get competent at that, exploring and observing you chakras should be relatively simple. A novice with a teacher should be able to get to that point within 2-3 months, without a teacher but with books within 6 months tops.