What we are (more or less) telling the browser is: at the <b> start making things bold, and at the </b> stop making things bold. Or, maybe a little more accurately, we are suggesting to the browser that all text contained within the <b>element should be rendered bold.
This is an example of nested tags. If you are going to use tag pairs in combination (which you will probably be doing quite a bit), then to avoid confusing the browser (not to mention confusing yourself) they should be nested, not overlapping. Let me illustrate...
