As discussed in Introduction and Overview, one way to approach an understanding of Manhattan's modules is to consider "lines of communication". That is, "Who can post messages in the module, and who can read those messages?"
The Handouts/Notices and Lectures modules provide one-way communication from you, the teacher, to your students. Only the teacher can post messages to these modules. Your students can read the messages, but cannot reply or comment on them, at least not within those modules.
Besides having different names, the Handouts/Notices and Lectures modules are exactly the same. The reason for having two areas with the same capabilities, but with different names, is simply to add a higher degree of organization to your virtual classroom. The Handouts/Notices module is a good place to put things like the course syllabus, reminders, schedule information, and announcements. The Lectures module, on the other hand, is a good place to put materials that are designed to teach. Examples of what you might find in the Lectures module include PowerPoint and other multimedia presentations, lecture notes created with a word processor, web pages you have designed, or even audio files containing your spoken words.
Handouts/Notices and Lectures are the most basic modules and thus are a good starting place for learning how to effectively use Manhattan.