Look in the root of the project for a gradlew file. If it exists, you can use the Gradle wrapper to execute the build without installing Gradle. Learn how to use it here. If you want information on how it’s generated in the first place, check out the user guide.
If that file doesn’t exist, you’ll need to install Gradle. The user guide explains how to do this generically for all platforms.
That’s not the only way you can install Gradle, though, the following links provide alternative approaches:
Detailed guide on installing Gradle on Windows (blog)
Installing Gradle with GVM (requires bash or zsh)(video)
Installing Gradle with apt-get on Ubuntu (blog)
Installing Gradle with Homebrew on Mac OS X (blog)