how to use can and could

can prevent tense and could is past tense capacity request and permissions can I sit here I can do it I could this work

Can & could are modal verbs. They are used to indicate the modality like ability, request & permission. Can: I can swim(ability) Can I borrow this pen?(request) You can go to the part(permission) Could: Could you tell me the time?(request) She could be there by now.(certainty) You could call them.(suggestion)