You insert dynamic content into your messages using dynamic content tags. There are around 70 of these and they are all listed in Appendix A of this guide.
For example, if you want to insert your subscriber's first name into a message, you would insert the dynamic content tag {FIRSTNAME <default>}. Your subscriber's email address can be inserted with the {EMAIL} tag and their unsubscribe link can be inserted with {UNSUBSCRIBE_LINK}