An op-amp is used as an oscillator in this LED flasher circuit. This is another circuit that can easily be built on an electronic breadboard by beginners in electronics. Click the above link for the circuit diagram.
This circuit uses a 555 timer IC and produces a fixed frequency audible tone that is played through a loudspeaker. No amplifier is necessary as the 555 puts out a signal of high enough amplitude. The circuit is easy to build for beginners in electronics and can be built on an electronic breadboard. Click the above link to find the circuit diagram.
In this article, a four LED light bar is driven using an Arduino Uno. Click the link to read the article, see the video and get the Arduino sketch.
If a buzzer operates from a low enough voltage and draws low enough current, it can be interfaced directly to an Arduino Uno pin. The article shows the circuit diagram of a buzzer connected to an Arduino.