Be careful: Use "was able to" for I and he/she/it but use "were able to" for you, we and they.
Questions: Put "was" or "were" or "could" at the beginning of the sentence followed by the person. For example: Were you able to win the prize?
Negations: Form them by using "wasn't/ was not" or "weren't/were not" or "couldn't/could not". For example: I wasn't able to come.