A "continuum" is a continuous series with no gaps or breaks in it. For example, the rainbow is a kind of continuum of colours going from red to purple with no gaps, continuously changing from one colour to another.
The natural numbers between 0 and 1 are also a continuum, because between 0 and 1 are 0.1, 0.2 etc. Between 0.1 and 0.2 are 0.01, 0.02 etc. There are no gaps in the series, the values increase continuosly.
The poles of a continuum are the end points. For example, some people say that political positions are a continuum. "Left wing" and "right wing" are "poles on a continuum". "Authoritarian" and "liberal" are also "poles on a continuum".
So the meaning of the original sentence is:
There are two opposite methods, but we do not have to choose one or the other, because there are many positions between them. For example, we could choose a method which is 70% A and 30% B, even though A and B are opposites.