The most common use case is where ARM provide fully functional CPU core IP that you can put into your own SoC - in AWS Graviton's case that seems to be the ARM Neoverse line of cores.
You can also get architecture licenses where you can implement your own CPU core (from scratch, or by making tweaks to an ARM design) - Apple has one of these, but Apple is a special case in that they were one of the original partners when ARM was originally founded in 1990.
RISC-V on the other hand is an architecture that is open for anyone to implement, but the RISC-V foundation doesn't sell you a core design - you need to create your own, or find a partner to sell you one. It's also much newer, so there's less of an ecosystem around it compared to ARM.
You can also get architecture licenses where you can implement your own CPU core (from scratch, or by making tweaks to an ARM design) - Apple has one of these, but Apple is a special case in that they were one of the original partners when ARM was originally founded in 1990.
RISC-V on the other hand is an architecture that is open for anyone to implement, but the RISC-V foundation doesn't sell you a core design - you need to create your own, or find a partner to sell you one. It's also much newer, so there's less of an ecosystem around it compared to ARM.