Here are some synonyms for "capable of being understood":
* Understandable
* Clear
* Cogent
* Comprehensible
* Intelligible
* Meaningful
* Perceptible
* Sensible
Here are some examples of how it can be used:
* "The instructions were not capable of being understood by a novice."
* "His explanation was capable of being understood even by someone with no prior knowledge of the subject."
* "The painting is capable of being understood on multiple levels."
Essentially, it means something is accessible to the human mind.