Many and much merge in the comparative and superlative forms, which are more and most for both determiners. It was once common to use the indefinite article with many (very a many years ago), as it still is with few (a few good men). However, this has fallen out of favor except in formations such as "a great/good many."
The meaning of MANY is consisting of or amounting to a large but indefinite number. How to use many in a sentence.