As I mentioned in another recording unstressed vowels in English sometimes end up with the schwa “[ə]” sound. This can lead to the written forms and spoken forms seeming very different. I’ll show you some written forms (which you could use in speaking if you want to emphasize every syllable) and spoken forms (which can be used in chatting or texting).
“You should have studied harder for the test.”
“You shoulda studied harder for the test.”
“I could have been a doctor if I wasn’t afraid of blood”
“I coulda been a doctor I wasn’t afraid of blood”
“I would have invited you if I knew you were in town.”
“I woulda invited you if I knew you were in town.”
Note: even many native speakers get confused with the written forms of these ones. The contracted forms “Should’ve, could’ve, would’ve” are often misspelled as “Should of, could of, would of”. If you see this, it is wrong.