I recently bought a MacBook and found a problem I can't open some videos on it. I'm just not really tech-savvy and don't understand what the problem could be. 

Well, most likely you just do not have a video player that can play all video formats. All Macbooks used to have Adobe Flash Player, but now you have to look for an alternative. You may find this article helpful: https://mac.eltima.com/flash-player-alternative/  . In fact, this problem is easily solved, the main thing is to choose a good video player that can produce all videos. The main thing to look that this video player had good reviews and that it is constantly updated.

Well, such problems are not only on the MacBook, but I also have an Asus and it originally did not have any applications that could be used to open the video, so I have to look for it.