I don't whether this will make things better or worse but ....
Differential calculus is what Nick is talking about.
Differentiation is how one property changes with another and integration (i.e. integral calculus) is the reverse. I'll use a familiar example.
If we take the rate of change of distance with time (i.e. we differentiate distance over time) we get speed (i.e. Speed = distance/time). If we differentiate speed with time, we get acceleration (i.e. acceleration = speed/time and we know speed = distance over time) which equals distance/(time squared).
Therefore, if we integrate acceleration, we get speed and if we integrate speed, we get distance.
If you draw a graph with time along the x axis (horizontal) and speed along the y-axis, the area under the graph will be the distance covered. If the speed is constant, the the graph will be a horizontal line. However, the speed could vary but the area under the graph will be the distance. If the speed is uniformally increasing, then there will be a slope to the graph and this slope is the acceleration.
As a rough schoolgirl guide, I can remember that you integrate, you add one to the power and divide by the power (and add a constant!!). To differentiate, multiply by the power and take one off the power.
i.e. momentum = mass x velocity. This means velocity has a power of one. Therefore, to integrate it by adding one to the power means velocity is to the power of two i.e. squared. Divide by the power i.e. divide by 2.
This sort of maths (which I have dragged up from over 25 years ago) is best shown rather than read so if you can find a friendly maths teacher, it would help you no end. It is easy honest but not to learn by yourself.
Cheers
Whirls