For that I use camtasia... Its a very cool video authoring tool, easy to use... I'd be lost without it... That aside make sure you have a good microphone as that can ruin a great video when you have low quality audio... As far as microphones go I use Blue Yeti... Best of luck!
I've heard of people using Cam Studio (free). I use it for my training videos as I am not into gaming (except to make money from it). I use Wirecast on top of that by feeding one computer to the other (Cam Studio > Desktop Presenter - Telestream > Wirecast on 2nd PC) which then streams live to wherever I want and/or records to File.
I also can use Wirecast's overlays and other configurations to really make a nice looking show.
I am planning to start broadcasting on Twitch any week now myself.
I would be lost without Camtasia it does everything I need and more. If you don't want to pay for a screen recorder then you could try HyperCam or Ezvid and Windows 10 comes with its own screen recording software.
I often used camtasia studio! Your video after making in camtasia studio contain 4 file: capture my sceen, use my webcame, record microphone, record audio sytem!
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