This app was mentioned in 2 comments, with an average of 2.00 upvotes
It's all good :) I'm not an expert in photography or video by any means but I've worked in the fields in some capacity for years. I think a lot of people who never worked in film (as in motion picture film) don't automatically make the connection. DSLR video needs to be treated a lot more like film and less like a camcorder or whatnot. Live autofocus and depth-of-field aren't like what you see on camcorders so you need to set up shots and use some sort of follow-focus for smooth changes on the fly. And like with film, you typically record audio separately from video so all of those film audio techniques come back into play.
Sometimes I will use an external mic plugged into the audio input of the camera to have everything in a single file but it's often just as easy to use my external mic and a dedicated digital recorder like a Zoom H4n for audio and sync it in post.
I figure if you're using that mic (just googled it and see it's only USB) it will be easier and more effective to just record audio to your computer and video to the camera. Trying to capture live from the camera while also recording audio from the USB mic could be more trouble than it's worth.
Still, if I was looking to do DSLR video with computer-recorded audio from a USB mic, I'd just go with the clapboard method. I'm sure you could also use something like a phone app that flashes the screen and makes a simultaneous quick "blip" of sound. Here's one for Android and I'd imagine there are others on the Play Store or the Apple store if you use an Apple phone.
https://play.google.com/store/apps/details?id=air.quart.studio.digital.clapper
2: Windows Movie Maker is a perfectly fine choice for beginners. I also used Avidemux which is also free.
3: Audacity for audio editing, something like Digital Clapper for easier synching up video and audio.