How do i pronounce the word "cero"?
No puff of air? There's no difference in the way I pronounce the English "K".
Unless your pronunciation of English is very unusual, there are two ways that you pronounce 'k'. The difference can be heard by contrasting the k-sound in 'kill' and 'skill' (for example). In the former the 'k' is plosive (puff of air) while the latter it is not. The k-sound of Spanish is like that of 'skill'.
This from studyspanish.com c
The Spanish "c" has two separate sounds, hard and soft. When appearing in the combinations "ca", "co" and "cu", the hard Spanish "c" closely resembles the English "k" sound. The difference is that when pronouncing the hard Spanish "c" there is no puff of air, as there is with the English "k". When appearing in the combinations "ce" and "ci", the "c" is softer. Spaniards pronounce this like the "z", while Latin Americans pronounce it like the "s".