Even though most of the IDEs provide built tools inbuilt but in the real deployment we always have our build scripts.
The examples of built tools are: make, ant, maven, sbt
A build tool runs the build script - steps to compile and test your code. We generally define tasks which perform actions such as copying, compiling, substituting a variable, uploading, running test cases etc.
In new build tools such as maven and sbt, the idea of artifact repository has come into play. We define the dependencies along with versions in the build file and it downloads those from a central repository. So, you don't have to worry about managing the bundles of libraries on which your code depends.