Tide predictions are created by adding up the effects of potentially hundreds of factors like the location of the sun, the moon, and the benthic environment. These constituents are derived from analyzing past water levels.
You can think of each tidal constituent as a sine wave. For example, below is a single constituent, M2, or "Principal lunar semidiurnal constituent" for Monterey, California during the first week of 2018:
If this constituent, which measures the regular effect of the moon on water levels, were the only one that affected the tides, then tides would go up and down in a regular pattern.
However, once you add more constituents to measure more effects, it gets complicated.To simplify, let us take just four constituents and plot them for the same location:
Just for fun, let's take a look at all the defined constituents: