I have searched google but I cannot find a straight answer. I know how to make, export and import a PGP private and public key. They come out as a .asc file. However, on websites I often encounter .pgp, .sig and .key files for verifying if programs are legit. So,
What is the difference between .sig, .pgp, .asc and .key files. Also, how do I make and export a .sig file and .key file?