Internal Examinations are assessment which is conducted by the college under the guidelines of university. It evaluates the students during their class hours. Only subject teachers and the students are involved in internal assessment.
Whereas external exams are conducted by the universities in the respective college. Which are not evaluated by the teacher who has thought the subject, hence, only the university and the student is involved in it.
Now you must have assumed that external exams are more important because it is done by external teachers while Internal are easy and negligible because its done by your own teachers. BUT YOU ARE WRONG
If you are not able to perform well in external exams either you would get less grades or even fail, but you would get chance to attempt again and improve. Where as if you get less marks or fail in internal, you wont get another chance to improve. Hence, no matter how much you score in you externals you wont be able to clear your course unless you score well in your internals.