Ciao and Buon pomeriggio are Italian equivalents of 'Hello' and 'Good afternoon'. The interjection 'ciao' means 'hello' and 'goodbye'. It's pronounced 'chow'.* The masculine adjective 'buon' means 'good', and is pronounced 'bwohn'. The masculine gender noun 'pomeriggio' means 'afternoon, evening'. It's pronounced 'poh-meh-REE-joh'.
*The sound 'ow' is similar to the sound 'ow' in the English adverb 'how'.