When you are using a software like VirtualBox to have other operating systems installed on your computer, you tend to run into hardware issues along the way.
Nothing is quite as simple as you would hope it would be when doing something complicated like this.
One issue that many have is that their microphone doesn't work in VirtualBox.
Find out a few things that you can do that will help it work better.
You need to first make sure that your sound is working in your virtual machine.
If you don't have sound at all, your microphone might be working but you can't hear it since you can't hear any sound at all.
You need to to VirtualBox's settings and set the host driver and controller to different settings.
Sometimes it's hard to know which ones your computer needs.
You can go online and search what settings are best for your computer or you can just guess.
Test each setting until you find one that works properly.
It will take a few restarts of your machine to get it right but eventually you will find one that works.
Turn on the microphone in your host system and test it.
You might have a problem with your hardware.
Your microphone or computer's microphone's port might be broken.
This is something you need to fix up before it will work in a virtual machine.
Make sure your microphone isn't muted in the virtual machine.
Normally under some audio settings you will see a muted microphone by default.
Make sure it's turned on so that you can use it the way you want to.
If nothing works, you might need to install a driver on your guest machine.
You can go online and download the driver for your guest machine's operating system.
Another option is to install the guest additions in VirtualBox which will give some of the audio and video drivers that you are going to need for the computer to function properly.