How can calculus be applied to real life?
Calculus is mostly useful in the fields of physics, engineering, and computer science. However, calculus finds - or can find - applications almost anywhere.
If you're ever going to do anything in any of those fields, even as a hobby, it's useful to at least know the fundamentals. But even if you're not, chances are that calculus had some impact in the past - and maybe just as much in the present - on your chosen profession.
Medicine? The rate at which IV drugs should be applied is often based on certain formulæ. Meteorology? There's an awful lot of physics involved in pattern prediction, and calculus is one of the least complicated bits of mathematics used. Machinery? Engineers had to build the tools and machines you use, and quite possibly with a heavy application of calculus for any and all moving parts.
Not to mention mathematicians, for whom calculus is just one tool in an ever-increasing toolbox of mathematical methods. If you're in any way fascinated by numbers, I'm sure mathematicians would love to have you join their ranks.