Question about Arabic articles?

If an Arabic article comes in the middle of the phrase then the 'a' drops out and it is replaced by a 'hamzatu-l-wl', correct? However, I don't understand if the letter connected to it is pronounced. For example: baabu-l-bayt..is the l pronounced in the middle of the phrase? Another example: 'al-walad wa-r-rajul..is the r pronounced in this phrase? And if so how am I supposed to pronounce a letter that has no vowel? :( Please help, I'm very confused..