The doubled p in appear is the ghost of a Latin prefix. The word is ad, "to," plus parere, "to come forth, be visible"; in Latin the d of ad assimilated to the p that followed, giving apparere, "to come in sight." English took the result through Old French aparoir and eventually respelled it closer to the Latin, keeping both p's. The word is a small demonstration of the rule that a doubled consonant near the front of a long English word usually marks a swallowed prefix rather than anything about pronunciation.
It arrived in the late 1200s meaning "come into view," which is still the core of it. The extensions are all medieval: to present oneself, as before a court, by the late 1300s, and — in the same years — to seem, to have a certain appearance. That last sense quietly reverses the first: to appear can mean to genuinely come into view, or to merely look like something.
appear (v.) late 13c., "come into view," from stem of Old French aparoir , aperer "appear, come to light, come forth" (12c., Modern French apparoir ), from Latin apparere "to appear, come in sight, make an appearance," from ad "to" (see ad- ) + parere "to come forth, be visible; submit, obey," which is of uncertain origin; de Vaan says from a PIE *prh-o- "providing." Of persons, "present oneself," late 14c. The meaning "seem, have a certain appearance" is late 14c. Related: Appeared ; appearing . also from late 13c.