[elisp] not clear why <let> uses 2 pairs of "( )"

[m2habert]

When command "let" is introduced it is not really explained why it evals through double parenthesis:

;; You can bind a value to a local variable with `let': (let ((local-name "you")) (switch-to-buffer-other-window "test") (erase-buffer) (hello local-name) (other-window 1))