When I say the words...
early, even, apple, able,
How can I learn how to pronounce them?
Have you tried this? Click English Pronouncing Dictionary with Instant Sound Free Online
After that you really just need to remember them because as you know, nothing is easy about English pronunciation. There are no hard and fast rules as English is not written phonetically.
This is how to pronounce them (using IPA)
early/ˈɜːli/ - the "r" sound is dropped in British English RP
It's interesting to note that both words beginning with E have completely different vowel sounds as do both words beginning with A.