Результат оказался хорошим.

Оказаться literally means “to turn out (to be)” or “to prove to be,” whereas быть is the basic verb “to be.” Using оказаться adds a nuance of discovering or realizing the quality of something after the fact. So:

• Результат был хорошим → “The result was good” (simple statement of fact).
• Результат оказался хорошим → “The result turned out to be good” (you learn or realize that it’s good, perhaps unexpectedly).

The verb оказаться is conjugated to agree with its subject результат, which is masculine singular. In the past tense, it takes gender and number endings:

• Masculine singular: оказался
• Feminine singular: оказалась
• Neuter singular: оказалось
• Plural (all genders): оказались

After verbs like оказаться, when you say “to turn out (to be) something,” the complement (predicate adjective) takes the instrumental case. The pattern is:

subject (NOM) + оказаться + predicate (INSTR)

So хороший (nominative) becomes хорошим (instrumental) to match this construction.

You change both subject and verb to plural, and keep the predicate in instrumental plural:

• Результаты (NOM, plural)
• оказались (past tense, plural)
• хорошими (instrumental plural of хороший)

Full sentence:
Результаты оказались хорошими.

Yes, if context makes it clear what you’re talking about. For example, after a discussion of several things you tried:

— Как был тест?
— Оказалось хорошим.

Here Оказалось хорошим implies “It (the test/result) turned out to be good,” even though результат is omitted.