• You can also launch the Settings menu within the Skype app by tapping the three-dot Menu button in the top-left corner. From the left-hand menu, select Help & Feedback, then click Skype Status to access the page in your browser.
• You may test your microphone (and speakers) in the app if your Skype microphone isn't working. Choose Settings from the three-dot Menu button, then the Audio & Video tab from the list.
• Speak into your microphone to test it. As you speak, the blue dots beneath Microphone should move.
• Try a test call whether everything above is working properly. To do so, open Skype and go to Settings > Audio & Video > Make a free test call at the bottom of the screen. You can also add the Skype user echo123 (called Echo / Sound Test Service) to your contacts list and use it as a test call.
• You should also examine Windows 10's privacy settings for camera access, just as you did with the microphone problem. Navigate to Settings > Privacy and select Camera from the left sidebar, which is located beneath App permissions.
• You'll have poor call quality if you  or anybody else on your network overloads your network bandwidth with heavy activity like downloading large files or streaming 4K video.

Read More: What is video messaging on Skype?