Modern science agrees that there are more than 4 dimensions, while they are not entirely in agreement as to how many dimensions we talk about.
According to modern superstring theory, the assumption of 11 dimensions makes the most sense, since it seems to explain a lot of open questions.
I recommend, if you are really interested in this topic, the book "The elegant universe" from Brian Greene, which makes a great attempt at explaining this highly theoretical concept in simple terms for non-scientists.
It stays a complicated subject in any case, and cannot be explained in a few words, just because our understanding is always limited by our three-dimensional thinking.
But it is a fascinating subject and certainly worth exploring.