When learning new words in English we might not be able to decode the pronunciation, especially if the word we are learning is a "sight word". Many online dictionaries provide an audio file for you to check the sound, but how do you know if you are doing it right.
First listen to the sound. Then, practice by copying the example sound.
When you think you have it record both the example and your voice. This is easy to do if you have a phone with a voice recorder or any other recording device. Simply press record, play the example sound and then do your best impression.
Play back the recording to confirm that you have it. You might be surprised how different it sounds.