The hypodermic needle model is a way of explaining how people can be influenced by media. It's like when you go to the doctor and they give you a shot with a needle. The needle is very sharp and it goes into your skin. When you get a shot, the medicine goes into your body through the needle.
In the same way, the hypodermic needle model says that when you watch or read something in the media, like on TV or the internet, it can go into your brain like the medicine from a shot. The media can influence the way you think and feel about things, just like the medicine can make you feel better if you're sick.
Some people believe that the hypodermic needle model is too simplistic because it suggests that people don't have their own independent thoughts and opinions. Instead, they argue that people are more complex and can think critically about what they see in the media, so they may not be as easily influenced as the hypodermic needle model suggests.