About the Pushbutton LED Circuit
the push button lets the electric current flow
How does the reed switch work
it closes near magnet
Segmented LED Explained
The top pins control four individual LED lights. All of the LEDs share the same positive prong (the middle) and all of the LEDs have their own negative prongs.
What is the terminal strip of the breadboard?
The middle holes are the terminal strip
How Buzzer Circuit Works
In the buzzer circuit the positive end of the battery is connected to the top bus which is connected to one of the long wires "tentacles". The other tentacle is connected to column 15 of the top terminal strip which is also connected to the positive end of the buzzer. The negative end is connected by a short wire to row 8 of the bottom terminal strip which connects to the negative end of the battery through the resistor. Therefore, if the two tentacles aren't touching, the circuit will be open, but if they are, it will close the circuit so current will get to the buzzer.
Multiple resistors like multiple dams
They add up
EEME Dad's comments: More accurately, the divide up the current in between themselves much like how a sequence of dams will hold back different levels of water as you go downstream.