When "new" [1] information is received that is fully compatible with the existing structures of knowledge, it can be threaded in with what is already known with little effort. This is our “preferred” way of learning, especially when we are adults, for a simple reason: it requires little energy. It also tends to reinforce the existing intellectual models we are already using; models which we have practiced using and with which we have some facility. This reinforcement strengthens the cognitive models, validates their content, further encourages us to continue using them, and gives us greater expertise in using them.
Generally, this learning involves interpolating the new knowledge into the existing structures, simply "filling in the gaps" of what is known. It may also involve extending the knowledge by extrapolating based on the existing structures. Though depending on the mechanism for this extrapolation, the new knowledge may be less structurally congruent with the existing knowledge.
Example: simply learning a new word in our native language would qualify for simple interpolation, unless it is a “borrow” work from another language, is a really long word, represents something outside of our experience, or requires complex enunciation. The new learning simply extends our existing vocabulary. Learning a dialect of a known language might be a form of extrapolation as long as the basic language structure is similar.
When studying the English language, having knowledge of Greek and Latin—from which many English words were derived—is well-known to assist in assimilating and understanding the meaning of new words and grammar in English.
FOOTNOTES
[1] Of course, by definition, this knowledge is not entirely new otherwise it would not be "...fully compatible..." with what is already known. There must be some significant overlap with existing knowledge. This means that, not only is the new stuff structurally similar, there is less to learn which makes the learning easier.