The important part of the quote is this:
we're trying to give you here an overview of this ... it's going to be a high-level more than other lectures,
In this context, "high-level" is a fixed phrase meaning the information provided is basically correct, but there are a lot of details, caveats, exceptions, etc. that are important for specific purposes but aren't necessary to get a basic understanding of the topic at hand.
See (eg.) the wikipedia description of high- vs. low-level descriptions:
High-level describe those operations that are more abstract in nature; wherein the overall goals and systemic features are typically more concerned with the wider, macro system as a whole.
Low-level describes more specific individual components of a systematic operation, focusing on the details of rudimentary micro functions rather than macro, complex processes. Low-level classification is typically more concerned with individual components within the system and how they operate.
In documentation, a high-level document contains the executive summary, the low-level documents the technical specifications.
The lecturer is saying that this particular lecture will be the "executive summary" of a variety of topics that will be relevant in the future, but won't be going into the technical details of any of them (but, future lectures will be going into technical details).
Of course, one can talk about a higher- or lower- level description, but that's usually in regards to a specific starting point. Since this is a lecture in computer science, a computer analogy:
A high-level description of a computer network is "a bunch of computers can talk to each other". Going "down" a level: "computers can share directories and printers, or can run services like web servers that allow other computers to interact with them". From there, one could go "down" to software protocols (NFS, HTTP, FTP, etc.) or to network details (TCP/IP, Ethernet, WiFi, etc.). Note that one could also reasonably talk about a high- vs. a low-level description of any of those; eg., HTTP "allows computers to transfer hypertext documents" vs. "uses a set of verbs to request that the server take various actions on the specified resource" vs. "... a 404 response code means that the resource wasn't found; a 405 code means that the method isn't allowed on that resource; ...".