Every camera in the world has a shutter button. The shutter button is the only button that you can press that takes a picture. If you are pressing a button on your camera and the camera is not taking a picture, that button you are pressing is not the shutter button.
If you press a button and the camera does take a picture, then that is the shutter button.
Only still cameras have shutter buttons. Video cameras have “record buttons” not “shutter buttons”.
Below is an image of a shutter button on an EOS RP:
The button is located in a place where it is easy to press with your index finger when holding the camera by the grip in your right hand.
Most cameras are setup for right-handed use, this means that holding the camera in your right hand is necessary in order to press the shutter button.
On many cameras the shutter button causes the shutter to open and close which is what allows light to enter the camera and hit the sensor or film.
Many digital cameras also have electronic shutters. And electronic shutter is what is used in a phone.
However, most professional quality cameras use mechanical shutters because a mechanical shutter actually helps the sensor perform better.
Below is a video of a mechanical shutter opening and closing on the EOS RP.
This type of shutter action is called “1st curtain electronic” shutter. That means that the first “curtain” of the shutter is electronically actuated, but the second curtain of the shutter is mechanical. This is still a little bit better than a full electronic shutter for image quality.
Now you know that the shutter button controls the shutter, and the shutter is the thing that opens to let light into the camera which the sensor than captures to produce a picture.
Film cameras work much the same way although they can have different kinds of shutters.
There are some very old-style film cameras that don’t have shutters at all. With those cameras the lens cap is the shutter, and the exposure time is usually very long, typically in the 30 second range.
Despite that, it’s safe to say that pretty much any camera you are likely to use will have a mechanical shutter button on it and pressing that button is how you take a picture.