Hi. Honestly, I don't really think there is a very significant difference. I believe "entender" is more common and "comprender" tends to be a little less common. However, both communicate the idea of understanding.

comprehend and understand, both synonyms, same meaning as in english.

Hi, it depends the context: about understanding or well known, they are synonyms. You can use either, for example: "entiendo lo que me dices" or "comprendo lo que me dices" entender= well communication between 2 persons.- "nos hemos entendido perfectamente" or " nos hemso comprendido perfectamente" on another context you can't use like synonyms, comprender= to hold many elements or contains.- "la ciuddad esta comprendida por muchas calles, casas y edificios" there are another cases, but in general this are the most important, only when your talk about understanding or knowledge can used like synonyms.

son iguales

You can use both as Synonyms :)