Manuka honey is just the same as any other honey except that it contains anti-bacterial ingredients (and costs a lot more!). It's main medicinal use is as a wound dressing (
http://www.bbc.co.uk/nature/28399182 ). Other than that you can simply consume it you would with any other honey, e.g. on hot, buttered crumpets (delicious!) or in a honey and lemon drink. The quantity you take isn't important (unless,of course, you're diabetic).