From watching those videos - it sounds like you’re in a very noisy environment. It sounds like there’s a lot of traffic noise from outside. Or the fan for your pc is running fast? Or perhaps you’ve got a room-fan, or air conditioning unit running in your room.
Whatever the background noise is, it’s loud and your mic is picking everything up. So if possible, you need to reduce the amount of ambient noise.
If the noise is due to sounds from outside, you will need to try to find somewhere quieter to record, or find some way of blocking more of the noise.
If it’s noise from your air conditioner/room-fan - perhaps consider turning it off whilst recording - which may not be comfortable, but it will reduce the noise!
If it’s the fan for your pc - I’m not sure what to suggest!!
Basically, try to reduce ambient noise in your recording space as much as possible, in any ways you can.
Another thing to consider - If your mic is omnidirectional, it’s going to pick up sound from all around you.
If it is possible to switch it into unidirectional mode (some mics have this capability), then it will only pick up sounds that are pointed directly at it. That might also help reduce background noise.
So try to reduce the amount of noise as far as its practical to, because your recordings will be better for it.
If there is no way of reducing the noise in the recording space, it’s not ideal, but it’s not the end of the world. Because even if you reduce the noise, you’ll never manage to prevent all noise in your recordings.
This is where an audio editor like audacity comes into play.
If you record the audio and video at the same time, you will need to use a video editor (like openshot, or kdenlive) to separate/isolate the audio track and export it from your video clip.
Then you can edit the audio in audacity and try to reduce the amount of noise. So perhaps try some noise reduction and compression filters... Before applying noise reduction, you will need to generate a noise profile from an area of your recording where there is no talking.
Once you’ve captured a noise profile, you can apply noise reduction to your audio and reduce the noise.
If there is a lot of background noise - it may be necessary to repeat the process a few times - take a noise profile from a blank area and apply the noise reduction again to further reduce the background noise until it is pretty much eliminated.
Here’s a YouTube tutorial that will show you how to reduce noise in your audio recordings using audacity:
It also shows you how to normalise and (optionally) EQ your voice clips.
Once you’ve edited your audio, you can re-import the new audio into your video editor before rendering out the final video.
If you record your audio separately from the video, then you can record your audio clips in audacity, use the tips in the youtube tutorial to improve the sound and then import your audio and video into your video editor and render your final video.
Either way works. Two slightly different workflows, but the end result is basically the same!