Regarding for .class files in Java

Hello All, I am trying to understand how .class files work in java and what's their purpose. I found some information online, but I get unsatisfying explanations.

When we run the program on online compiler here - https://www.interviewbit.com/online-java-compiler/ we get the .class file, which is bytecode. Is this machine clear or not? Also, on the off chance that not, for this reason we want the mediator for the program to effectively run?

Likewise, since the .class file is what could be compared to our .java programs, for what reason might someone at any point run a java program straight away simply by running the .class file utilizing VM and they could have to have the .java file too?