White Hat SEO technique means traditional on page and off page optimization points which you read everywhere like
1. creating relevant title tag, Meta description and keywords.
2. using your keywords with alt tag for images.
3. Use your keywords in <h1> and <b> tag.
4. Do social bookmarking, forum commenting, blog commenting and so on.
You can't exactly explain the black hat techniques but I can give you some idea, hope you can elaborate by yourself.
Using too many keywords or repeat your keywords in title, meta description and keywords tags, Placing your keywords on webpage while hiding it for your users, indulging in page cloacking technique.
Or you can say the seo techniques which oppose white had and genuine seo techniques, are black hat seo.