1) How quickly is something (population of aphids, sales of a new product, amount of water left in a pond) changing right now? and
2) How much total change has accumulated in a given time period?
And that's really the dirty little secret of calculus: there are really just two ideas at play. The first question takes up most of the semester and is known as 'differentiation' while the second takes up maybe 25% of the course and is called 'integration'. The end result can sometimes be called as beautiful as the music and art it has often inspired.