How to create a new key?

[svban]

I want to map capslock to enter, and shift capslock to '~'
How to do so?

[gerhard-h]

(fork ret (unicode ~) (rsft lsft)) or (fork ret (unshift (unicode ~)) (rsft lsft))
you may want to replace the universal (unicode ~) according to your language and OS

[svban]

This works -

(defalias
              rett (fork ret ` (lsft rsft))
)