can
Kann is the German equivalent of the English word 'can' when used to express ability or permission. It is a modal verb, and as such, its conjugation is irregular. For example, 'I can swim' in German is 'Ich kann schwimmen'. It is also used to ask for permission, as in 'Can I go to the park?', which is 'Darf ich in den Park gehen?' in German.
Can I have the book?
In German, 'Kann ich' is usually placed at the beginning of the sentence when asking a question, similar to 'Can I' in English.
Can I go to the bathroom?
This sentence is a polite way to ask for permission to go to the bathroom. 'Zur Toilette gehen' translates to 'to go to the bathroom'.
He can cook well.
In German, the verb usually comes second and the adverb usually comes in the last position. That's why 'gut kochen' (cook well) is at the end of the sentence.