Hope you don't mind my quoting from a book, Soarer.
Old English had a system of long and short vowels and diphthongs...The short vowels have remained relatively constant over the centuries, so that many words are pronounced today as they were in Old English: fisc "fish", aet "at"...The long vowels, on the other hand, have undergone marked changes. Suffice it to say for now that Old English long vowels had their "continental" values, as in the following words: staan "stone"...
As to consonants, Old English permitted combinations of consonants that Modern English no longer tolerates, including initial hl-, hr-, and cn-....
Source: Language: its structure and use (by Finegan and Besnier)
Not sure how much you need to know. After all, this is not covered in the Form 7 curriculum....