E-Lock Circuit Help

For school I was assigned a madlab circuit, E-lock, to build and explain how it works, and to be frank, I have no clue how it works. I was able to build it and it functions as it is suppose to: using the frequency of the sounds emitted when you click the numbers on your phone keypad to light up an LED. But when it comes to explaining the different components and how they are used in the circuit, I’m lost. Any help would be greatly appreciated. I’m looking more for the surface-head scratch of how these components function.
Component list

• Resistors
• Diodes
• Chips and their sockets
• Electrolytic capacitors
• LED
• XTAL
• Transistors
• Regulators
• Connector
• Relay
• MIC
• Battery

Here’s the schematic (above) and the construction sheet (below)