You have a few options for doing this.
I recommend the third option as pulling content from WordPress into your existing site will cause some slowdown of your site. Unfortunately, none of the options can be easily explained and you really have to do some reading on how to accomplish all three. If you Google "integrate WordPress into existing website" you'll turn up a lot of other people who have either asked the same thing or have tutorials on how to do it.
If your blog has an RSS feed (which almost every blog does), you could parse all or a portion of that feed into your main site with a freely available PHP script.
I describe how to do it with a Blogger RSS feed below.