I recorded a video but it had no sound, so I want to add sound, audio into the video, of courses the sound, audio will be at a specific time not the whole video will have sound, audio (The video is 10:00 minutes, so I want to add sound at 4:00 and 6:00, and the rest of the video don't have sound). I have heard about the built-in video software on Windows, is this work? If its not, is there any easy software that can do my requirements? Thank you!
Windows Movie Maker can do this (or the Photos app, depending on which version of Windows you're on). It's not the best program, but it works. There's a guide on using Windows Movie Maker to do that here about halfway down, and using the Photos app here.
You can also do it on the command line with ffmpeg which may be more efficient once you're used to it. An example would be
ffmpeg.exe -y -i the-video.mp4 -itsoffset 00:40:00 -i the-audio.mp3 -map 0:0 -map 1:0 -c:v copy -preset ultrafast -async 1 output-file.mp4 (source).