Investigate filter circuit using operational amplifier?

A filter can be designed using an op amp by by replacing the resistors in an inverting or non-inverting amplifier with inductors or capacitors. Search for "op amp" on wikipedia for some simple schematics as a starting place. If you understand the basics of filter output and bode plot calculations, you should be able to replace R1 or R2 with C1 (1/jC1w) or L1 (jwL), and analyze the output vs. input characteristic.

Note op amps have limitations on frequency response, so this approach is good for fairly low frequencies - if you get into the high MHz, or GHz, a passive filter circuit becomes necessary.