Every person comes to college level math with a different background of formal studies and comprehension. Most sites that provide math review, therefore, generally span a range of topics from basic arithmetic to calculus. Mathematics has its own symbolic language and logic.
Some people quickly grasp the language, others have to work much harder.
Generally speaking, you will be expected to know arithmetic, beginning and perhaps intermediate algebra, basic geometry, basic trigonometry, and simple statistics. In addition you should also be able to understand standard charts and graphs and analyze their meaning. You may find it useful to gain an overview of mathematics by reading entries in any good encyclopedia. Almost everyone reaches a point that they don't understand in these encyclopedia entries. That is natural and should not lead to panic.