It must be 20' talk, right? This is what I had in mind, trying to introduce the feature for people that are new to C++11 and "modern C++", but I have to assume some prior programming and C++ knowledge:
lambda expression (simple, without captures at this point) in relation to a typical function definition and use
what they return
some simple use case (and some personal experiment)
relation to function object (I want to use this to explain the next, I need to assume that this concept is known to save time)
capture list, first by copy then by reference
warnings about dangerous situations with capture by reference
at some point but not sure yet where, I should mention "mutable lambdas" (it drove me crazy not having understood at the beginning that they are const methods by default)
Sounds good. Your talk should be 15–25 mins long. So aim for 20', yes.
You should assume your audience has C++ programming experience but might be stuck in a pre-C++11 and pre-templates world. This doesn't mean you have to start at 0, but you should be prepared to accommodate clarifying questions.
relation to function object
For completeness you should note that lambdas without capture list are convertible to function pointers.