Okay, imagine you are playing with puppets - little dolls that look like people or animals that you can make move and talk. Now, imagine having a special kind of puppet that looks just like you, but it's really still just a puppet. This is kind of like what people mean when they talk about a "sock puppet."
A sock puppet is a fake online account that someone creates to pretend to be another person or to say things that they don't want to say using their real name. They might use a fake name, fake picture, fake information, anything to make it look like a real person. They might even pretend to be someone else, like a celebrity or a politician, to try and trick people.
Sock puppets can be used to do all sorts of things. Sometimes people use them to praise themselves or their work, to make it look like other people are saying good things about them. Other times, they use them to attack or criticize other people, to make it look like there are lots of people who agree with them. In either case, it's not really fair or honest, because it's not a real person saying those things - it's just a puppet.
So, to sum it up - a sock puppet is like a fake online person that someone makes up to pretend to be someone else or to say things they don't want to say using their real name. It's kind of like playing with a puppet that looks like you, but it's not really you.