Ronnie is teaching us how to make the right pronunciation of CAN in the affirmative with an American accent. For British English, the pronunciation of CAN is more or less the same, but it sounds /kən/, not /kɪn/. For the negative, though, in American English it is /kænt/ or /ke:nt/ and in standard British English it is /kɑ:nt/. Remember that in the negative form the final /t/ is often dropped, so we have /kæn/ or /ke:n/ or /kɑ:n/, that's why it is important to use the /kn/ version for the affirmative.

Just remember the idea of considering the affirmative just one word: Ican, Youcan, Hecan... so the verb is not stressed.