To start, you're going to want to add ProtocolLib as a dependency to your project. While you could download the jar file and add it as a classpath dependency, we highly recommend using a build system such as Maven or Gradle.
Maven and Gradle should download the JavaDocs. If not, you can find them here: https://ci.dmulloy2.net/job/ProtocolLib/javadoc/overview-summary.html
Maven
<repositories>
<repository>
<id>dmulloy2-repo</id>
<url>https://repo.dmulloy2.net/repository/public/</url>
</repository>
</repositories>
<dependencies>
<dependency>
<groupId>com.comphenix.protocol</groupId>
<artifactId>ProtocolLib</artifactId>
<version>4.7.0</version>
</dependency>
</dependencies>
Gradle
repositories {
maven { url "https://repo.dmulloy2.net/repository/public/" }
}
dependencies {
compileOnly group: "com.comphenix.protocol", name: "ProtocolLib", version: "4.7.0";
}