Trigonometry can be understood as the study of triangles and their relationship to geometry. This category of mathematics studies angles, lengths, sides of triangles (typically right triangles) and trigonometric functions necessary to understand relationships of triangles.
Yes, of course. Your teachers may tell you trig is necessary to pass pre-calculus and calculus and any consecutive courses you may choose to take. This really isn't a convincing reason to take any class. In the spirit of math, let's look at this in a real-life application:
Suppose you want to install the coolest ramp in your driveway made of 2x4's and plywood for all your neighbors to skateboard on. You've got the 2x4's purchased, and a design for height and horizontal distance. The best condition for beginning skateboarders happens to be a 3 foot tall platform, with 4 feet of horizontal travel distance. How would you know that you need 5 linear feet of plywood to complete the deck of the ramp?
Well if you've finished up trigonometry you would be able to tell what angle that ramp is (36.9 degrees), or how much wood you need to purchase for the hypotenuse of the ramp (5 feet). Although a firm understanding of geometry would also help you to understand a lot of these concepts, trig takes it further and helps you understand the equations behind these geometric shapes.
Below is an intimidating list of all areas of Trigonometry; don't sweat it if this looks like a foreign language. Take the topics one at a time (they go from easy to blazingly difficult), and you may find the subjects build upon one another, just like your teachers explained in every math class you've ever taken.
You can rely on your knowledge from past math courses, or you can browse the collection within the math^2 website to help brush up on any related subject matter. Let's get started!!