If you are using windows 10 Win+Alt+R to start your recording. Will record what’s on your screen including audio (test this before you need it for a lecture) on a Mac I use QuickTime and record the screen.
TheBig40 nails it and you should test your screen recording ability beforehand. But usually the lecturer will record it themselves and post on Moodle however that is their decision, and might depend on what resources they have available to them... Not that many organisations are still using Moodle because the user experience can be a bit clunky, but it is "free" and has good community support see https://moodle.org/course/