For software to run on a computer it needs to speak the computer's "language". This is typically called "machine language" but differs across different hardware. For example most modern Intel and AMD processors speak x86_64. This language has ways to express different operations such as "add these two numbers" or "put this CPU core into a low power mode". This is the fundamental way that software works, but running in this language.

There are languages that are completely different, such as ARM which is very common on mobile devices and is the language used by Apple's new M chips. These have basically nothing in common with x86_64.

These languages also evolve over time. For example x86_64 is a significant extension to the older x86 language. For the most part this is fine, it is like the CPU now knows more words, if you use those new words the new CPU will understand them, but older CPUs won't.

RISC-V is a new machine language. What makes it interesting is that it is a free and open specification. This means that anyone can create a new RISC-V CPU, unlike x86_64 where you need to buy a license from Intel or ARM where you need to buy a license from the ARM corporation. Most people think that this openness has major benefits, for example now anyone can create a new processor which may be better, rather than having innovation being stifled by licensing costs (if you can even get a license) or needing to create their own machine language and require huge amounts of effort to migrate software to it.

Note: It is important not to confuse "machine language" with "programming language". When people write software they very rarely write code in machine language directly. Usually they use a programming language which is then converted into the machine language of the CPU it will run on.