Registration in Chat GPT is free, you just need to follow the link https://chat.openai.com/
There is, however, a catch: you have to register to a non-Russian number, and it is likely to work only through a VPN. But here the creators of the miracle machine is hardly to blame. Foreign numbers can be found through esim or by going on vacation to the neighboring republics.
Otherwise, the instruction for use - you can not think of easier: you register and start asking questions. That's it.