What is Scala's Simple Build Tool (sbt) and why is it used?

I am new in Scala and I have to learn Scala and SBT, I read the sbt tutorial but i am unable to understand the use of sbt, for what purpose its been used.After reading this tutorial I am still confused can any one will explain it in simple words, also suggest me if there is some tutorial for simple build tool

When you write small programs that consist of only one, or just two or three source files, then it's easy enough to compile those source files by typing scalac MyProgram.scala in the command line.

But when you start working on a bigger project with dozens or maybe even hundreds of source files, then it becomes too tedious to compile all those source files manually. You will then want to use a build tool to manage compiling all those source files.

sbt is such a tool. There are other tools too, some other well-known build tools that come from the Java world are Ant and Maven.

How it works is that you create a project file that describes what your project looks like; when you use sbt, this file will be called build.sbt. That file lists all the source files your project consists of, along with other information about your project. Sbt will read the file and then it knows what to do to compile the complete project.

Besides managing your project, some build tools, including sbt, can automatically manage dependencies for you. This means that if you need to use some libraries written by others, sbt can automatically download the right versions of those libraries and include them in your project for you.