Calculus

I want to learn calculus.  How and where should I start?

Britfag here
I understand the basic technical side of calculus, and what you're actually intuitively doing when differentiating and intergrating (with or without limits), but I dont understand the 'with respect to "whatever variable"'.

It would be appreciated if someone could give an overview of what it means, as its preventing me from understanding whats going on in the stuff im doing now.