、。
Help yourself to anything in the refrigerator.
Literal
Refrigerator [of-の] inside [of-の] thing [topic-は], anything [at-でも] freely help-yourself [please-召し上がってください].
召し上がる is the respectful (sonkeigo) form of 食べる/飲む ('to eat/drink') — elevates the listener's eating. 御自由に ('freely, as you like') uses the honorific prefix 御 (ご) on 自由 ('free') + に adverbial. ~でも after an interrogative = 'any-, every-': 何でも ('anything'). A polished host's invitation.