If I want the 'electric current wave' to flow in only one direction, then I would a diode. While choosing a diode I would take into consideration several factors such as maximum current flow allowed, maximum power, etc. In the end, electronics is more or less about how to manipulate that 'electric current wave' to do different things. The electronic components help us to use that electric wave in different ways. I hope you get the idea what I'm trying to convey.
Q1: Suppose I want an oscillator which produces, let's say, triangular wave. How would I find it? Could you please provide me a list of oscillators which 'graphically' shows me which oscillator produces what kind of wave?
Q2: Different amplifiers, such as differential amplifier and inverting amplifier, affect the input (or, incoming) electric wave in different ways and we end up with 'affected' or 'amplified' output (or, outgoing) electric wave. Could you please provide me a list which graphically shows how an amplifier (such as op-amp) affect its input wave?
Look in Google for Triangle Wave Circuit. Many links show a circuit with one opamp as a Schmitt-trigger and a second opamp as an integrator.
When you learn about electronics then you will recognize a sine-wave circuit, a triangle-wave circuit and a square-wave circuit.