Many interesting audio effects are achieved by combining a sound with a delayed (and possibly altered) version of itself. To delay a sound, one needs to store it for a certain amount of time till (a delayed copy of) it is needed. That storage has to be constantly ongoing when we’re dealing with realtime audio processing, yet we usually also want to dispose of the delayed audio data once it’s no longer needed. Realtime delay of audio is therefore most often achieved by storing the sound in what’s commonly called a ring buffer or a circular buffer.

In MSP a circular buffer is implemented in the delay~ object, and also in the pair of objects called tapin~ and tapout~. Here are some examples from a previous class.
Simple delay of audio signal
Delay with tempo-relative timing
Simple flanging
Delay with feedback

There are some MSP Tutorials that deal with delayed sound. [The links below are to the web version of the documentation, but you’ll probably prefer to use the Reference documentation within Max so that you can try out the tutorial patches while you read about them.]
Delay Lines
Delay Lines with Feedback
Flanging
Chorus
Comb Filter

And here are some more examples from a past class.
Change of delay time may cause clicks
Continuous change of delay time causes a pitch shift
Ducking when changing delay time
Abstraction for crossfading between delay times
Demonstration of crossfading delay

Filtering is a special case of delay, using extremely short delay times to create interference between a sound and a slightly delayed version of itself, which causes certain frequencies in the sound to be attenuated (lessened in strength) or resonated (increased in strength), changing the sound’s timbre. [These are links to the web version of two MSP tutorials; you may prefer to read them in the Max Documentation within the Max application.]
Simple filters
Variable type filters

Here’s a very thorough tutorial on filters in MSP written by Peter Elsea.

And here are some filter examples from a past class.
Bandpass filter swept with a LFO
A variable-mode filter: biquad~
Smooth filter changes