PHP and MySQL are server side programming languages that allow us to put interactivity onto our sites. This is extremely useful because it keeps a user interested in our site and also allows us to collect information through the Forms we put on our websites. Users can input data into surveys, post their comments, provide reviews, etc. With a PHP form capture. The information is then stored in our database. PHP strings also allow us to create CMS or content management systems.
This is what the computer geeks are talking about when they say dynamic content (I think). Basically what it means is we can store our articles, images, videos, CONTENT, in our databse and have it displayed under certain conditions. This adds lots of versatility to a site and allows us a way to have our USERs start creating content for us IE article directories.

I am working my way through an e-book about php right now that I will post to this tutorial once I determine its value. PM me and I'll be glad to share it with you

The databases are where all our info is stored and we need to code our communications with the databases as well. MySQL is the most popular database language for websites. Databases are places to store MASSIVE amounts of information that we can collect about our users. Collecting Customer Information is extremely useful for us since it helps us target our offers to our email list even more effectively.

For instance, in the dog training niche, there are probably many products that are appropriate for small dog owners that aren't appropriate for big dog owners. The owners will have different concerns and it helps us as marketers if we can break our list down with the info we have in our databases.

I outsource all my PHP and MySQL work since, to me, it still seems very complicated. But it does help to at least appear to know what you're talking about when dealing with programmers.