क
It is written as follows

It is pronounced as ‘K’ in the word as in ‘Speak’. It is not an aspirated sound like that of English means there is no air released while speaking it. Its sound is short. Hindi letter क in romanization it would be represented as K.
For Example:
कप is read as KAP (Pronounced as Cup in English) in Hindi which means Cup in English.
कल is read as KAL in Hindi which means Tomorrow in English.
Practice reading the following words.
कलम KALAM Pen
कब KAB When
कमल KAMAL Lotus
ख
This letter is written as follows

This letter is closely sound as C sound in ‘Cup’ of English but it is strongly aspirated than English. This is aspirated version of the letter क of Hindi. That means you would feel the air releasing while pronouncing this word. You would feel some vibration in vocal cords while pronouncing this word. Some other similar sound in English are as ‘K’ in Skip in English. So, in romanization we would be using Kh.
Some examples in Hindi are
खत Khat Letter
खबर Khabar News