Okay kiddo, have you ever seen a special type of bottle that has two different parts, one on top of the other? That's called a Schlenk flask.
The bottom part is usually made of glass and it's where we put the stuff we want to do experiments with, like chemicals or reactions. The top part is usually made of rubber, and it has a stopcock or valve that we can use to control the gases that go in and out of the flask.
Now, why is all of this important? Well, some experiments need to be done in a special environment, like without any air, and that's where the Schlenk flask comes in handy. We can use it to create a vacuum or a special gas atmosphere, like nitrogen or argon, which helps us keep our experiments safe and accurate.
Overall, a Schlenk flask is just a cool tool that helps scientists do experiments in a controlled environment.