The LIVE lecture is just a lecture.
It is very freeform according to the magician's tastes. There is a live audience of magicians, a host (usually Dan Harlan) and the secrets and tricks are usually the focus. The format tends to be trick, reveal, trick, reveal, etc. Sometimes the magicians would mix in more information or deviate from that format but that's generally
The LIVE Acts are a lot more specific.
They usually start out with a 15 to 60-minute complete act performed in front of a live audience. You watch the entire act without any cuts and then the magician breaks it down. Most of the lectures get really detailed. They mention each piece and how to obtain the props. They discuss the way they organize their props and why they chose the material they do in performance. This explanation portion is not usually in front of a live audience, it is usually just Dan Harlan and the magician. When you order a LIVE Act you get tricks and how to perform them, but you also get a complete professional act that you can start with as you create your own act.