Actually, being like a computer game is probably what you want to do. Modern (and even classic) video games try really hard to not be brutally hard and kill the players at every possible chance. You should try to strike a balance. Too hard, and players will die a lot. Too easy and they will get bored.
In most games, the story is centered around a few exceptional characters that do exceptional things. Making them feel exceptional is important and surviving against poor odds is part of that. However, not all games are focused on exceptional people and not all stories end with the hero on top.
PC death is something that needs to be discussed as you start planning your campaign with the players. Everyone needs to have the right expectations about the survivability of their characters. Part of this choice will be expressed in the game you chose to play.
Games like Call of Cthulhu and Shadowrun are notorious for killing off PCs very often and have rules in place for making character generation and having new characters join the game pretty easy to do. While other games don't feature character death as a randomized element at all.
Another part of this choice will come down to the feelings of the players and what makes for good story. Sometimes it fits the story for a character to die. A great sacrifice is sometimes the best way for a character to meet their end. Death in battle is sometimes the only way for some characters to go to a favorable afterlife.
Problems with PC death occur when a group is not all on the same page or when the death is cheap and too random. In only the most brutal or realistic of games should PC death be trivial or happen as the result of a single die roll. The classic meme of "Rocks fall, everyone dies" is really a symptom of poor Game Mastering in most cases. And when those deaths cause significant friction in the group, it is always poor GMing. If real risk of death is something your players want as part of the game, make sure that only a consistent disregard for safety practices or very bad choices are what lead to death. Make it an inability to recognize when they should run, or running into an obvious ambush alone the cause of death.
The major takeaway from this should be that frequency and the circumstances of PC death need to be a group decision. It is fine for your game to feature regular PC death provided the group as a whole wants it.
One technique I would suggest for new GMs is to build encounters that can have additional enemies or threats added during the course of the encounter. For example, if the party is fighting a bunch of zombies that rise from graves, leave 2-3 graves filled and only raise those zombies if the battle looks too easy. Another option is to be prepared for the enemy to not want to kill the party, but rather capture them, or just steal their stuff.