I'm sorry for the big text, but that's it!
So friend if you record videos on your computer, type gameplay or video tutorials, you can use Audacity to record the audio, in it you can monitor the volume of your voice in case you are popping the audio.
To record videos on your computer, you can use OBS or Open Broadcaster Studio, it is a free and very good software for both recording and live broadcast.
For you to do the Thumbnails in your video, you can use GIMP which is free and very good for this kind of more "basic" work.
And for the editing of videos has no way, the right is you buy some program, but if you use MacOS, you can opt for iMovie it is free, for windows it is very rare you find such software and free.
Well, I guess that's it, I'm sorry for my English.
All the best and success for you my friend!