[noun] + しか + [verb (negative)] [noun + particle (を/に/へ/で/から/まで etc.)] → particle replaced by or combined with しか + [verb (negative)]
[verb (dict)] + しか + [verb (negative)] [verb て form] + しか + [verb (negative)]
[counter/quantity] + しか + [verb (negative)]
しか always requires a negative predicate (〜ない / 〜ません etc.)
The grammar structure ~しか is used to express exclusivity with a negative nuance, meaning "nothing but" or "only." It emphasizes that there are no other options or possibilities beyond what is stated. Importantly, しか must always be followed by a negative verb form.
Unlike だけ, which is neutral and allows for other possibilities, しか conveys a stronger sense of exclusion and implies that no other options exist.