cert.pem and key.pem

I am using my raspberry pi to create a server. I want that server to be accessible through

ws://server.stio.studio

ws://server.stio.studio

ws://server.stio.studio

ws://server.stio.studio. I am nodejs btw
For now I have found out that I need the

cert.pem

cert.pem

cert.pem

cert.pem and

key.pem

key.pem

key.pem

key.pem files to connect to my domain. How do I get them or is it another way?