How does a light switch work?

When you turn a light switch off, it "opens" the circuit and the electricity does not go to the light. As you suggest, the current is "blocked off." Turning off the switch is like closing a door. No one can come in.

Turning on a switch "closes" the circuit and the electricity goes to the light. The light will come on.

The hardest part of this to understand is that a "closed" circuit means that the electricity is going to the light -- nothing is interfering with the flow of electricity. An "open" circuit means that there is a break in the flow of electricity. It is kind of the opposite regarding the door analogy! A closed circuit is like an open door and an open circuit is like a closed door!

If you plan to replace a switch, definitely turn off the power at your entry panel!

Nice Q. Mentally, it's a little like a valve on a pipe. Shut it off and the water/current stops flowing. A step further in needs a little understanding of a "conductor" for electricity, in this case typically a run of a good one, like a copper wire. Electricity will just zing along through a conductor, unless that path is stopped. A switch, in effect, takes a little bit out of the path, again mentally kinda like a draw bridge: move or lift a part of the path, everything stops. Put it back in place, flow resumes. Inside the switch, moving it to "off" temporarily breaks the conductor path, separating contacts which are then put back in place when turned it's turned "on". The actual size of those contacts can be quite small. That's pretty much it.

Connect-disconnect. Those are the two positions.

Maybe if you saw an old "knife switch" it would make more sense.

"Blocking" is not the right word, or the right way to envision how it works.

Look at the photo of the "open knife switch":

https://en.m.wikipedia.org/wiki/Knife_switch

The open knife switch is in the "off" position.

Usually there are two metal parts that touch when the switch is turned on.

How Do Light Switches Work

https://www.youtube.com/watch?v=i94ztd5D7VM explains the basic principals of switches. Watch it and learn, but unless you know how to deal with electricity properly, DO NOT try to do any electrical work yourself. It stings at least and kills at worst! You aren't different than most people in the world when it comes to understanding electricity. It is still akin to "magic" to most! It's good that you want to learn.

A light switch works on the principle that relatively low voltages will not "flow" across an air gap of sufficient width. When the switch is "open", the metal parts are separated by air (or some other insulator) that stops the flow of electricity. When the switch is "closed", the conductive parts are places in contact with each other and allow the electricity to flow, assuming the rest of the circuit is also "complete".

You have a hot wire to the light and above that you run a wire over to the switch. It is wired hot and so when you turn the switch off it breaks the line and no electricity should go to the light. Turn the switch on and it completes the circuit and the light goes on. There are two ways to wire this.

electricity comes from the wires in the wall, which come from outside the home; the inside wires go to outlets & wall switches; when a switch is turned on, it completes the electrical circuit; when the switch is off, the circuit continues on to the next switch or outlet

You push it with your hand