If you want to say someone is easily scared, you would say, "He is easily scared." Your versions above are not used in English.

"He scares easy" is an incorrect statement, and used colloquially or in informal speech. "He scares easily" is the correct statement to write down. You can turn most nouns into adverbs by adding the "-ly" ending to enhance the verb. "Easily" describes how the subject "he" is scared. Because there is no "-ly" ending in the first sentence, the first one makes no sense.