What are "single player games"? Single-player games are games intended for one person. Only one person can play this game ... by themselves ... by themselves. For people who may be socially shy or awkward, don't speak the majority language for this game, or are too young to interact with others, this can be a good thing.
With single player games there is no need to worry about predators, stalkers, young people who see nudity, hear language, are bullied, harassed, verbal abuse, losing content or interact with others. You can just enjoy your game without worrying about the world. So you really don't have to worry about much since these games are for one person only.
Just because you might be the only one playing the game doesn't mean there's nothing to be careful about. While most of the negative things about all types of games come from some real people in those games, some of the negative things are from the type of games and types of games for the wrong person.
There are a lot of horror games, games with nudity, language, intense subjects, intense scenes, smoking, drugs and alcohol, gambling with money real, suggestive themes, blood and blood, games that have violence, etc., which are just for one person.
You really need to look at the game's website, social accounts, videos, images, description, tags and most importantly the reviews. You need to gather all the information about the game you are planning to buy, whether it is for yourself or for someone else.
If the game is on Steam, Humble Bundle, or some similar websites; they will show you the description, videos of that company, images, user and non-user tags, user reviews, website, company and social accounts. However, if you are on the game's website, they may not display everything you need to know to decide whether or not to buy the game.
The least some game companies show is a very short description of the sales pitch, a small amount of images (5 at best), a video or two from them and their social accounts. The most they will show is an informative description, photos of them and users, user reviews, videos of them and their social accounts. I'm not going to go into the good and the bad in the game and how to tell if the game is good or not in this article is another article.
Now you would think all games would have a single player mode and then add more modes later. After all, it's a little easier to have players play on their own and create a new world or file than it is to pay that many dollars a month or year to host a server, have problems getting and maintaining the server, then have the players actually connect to the server. At first you would think that some games will add a single player mode before adding co-op or multiplayer, right? FALSE!
There are a lot of games that only have multiplayer, co-op, and any other non-single player mode. Some games are only intended for multiplayer, such as MMOs (Massively Multiplayer Online). Multiplayer games can be played with more than one person on a computer in the same room, but most people call it Local Multiplayer or Local Co-op. This allows you to play with someone on the same computer in the same room.
You can't play with someone from Sweden if you're in the US in local multiplayer or local co-op. You have to go online for this. It's the same as the way you talk to people all over the world from Twitter, Facebook, Discord, Skype, etc. which are all online. If your internet connection is down, you cannot talk to anyone on these platforms because it is not online.
There are many types of games and game modes for different people. You can get a strictly single-player game or a game that is both single-player and multiplayer and play solo for the time being. Some people like the game and not the multiplayer part, so they only play the single player part. I recommend starting with single player mode and then getting a game later that has both so that you can get comfortable with multiplayer versus multiplayer.