They have the same meaning. In English we have many pairs of words which are near-synonyms, one with Germanic roots and one from Latin roots. In most cases, the word with the Germanic origin is a commonly used, everyday word, whereas the word with the Latin origin is used in more formal or academic contexts. This is the case with 'understand' and 'comprehend'. 'Understand' is a common word which we use all the time, whereas 'comprehend' is relatively formal, and used much more rarely. I hope that helps.