Erin Whelan’s inviting Lower East Side boutique Clarabella (279 E. Houston St., nr. Clinton St.; 212-979-0270) is like a classroom for retail education: Whelan likes nothing more than to explain to her customers the provenance and process behind her store’s handbags, jewelry, and shoes. Those close ties to the designers she sells means Whelan knows, for example, what inspired up-and-comer Cheyenne Morris (of Tashkent by Cheyenne) while designing her line of shoes (it was her grandmother; and the shoes start at $272) or how Annika Salame of By Boe put her dressmaking background to use for the beadwork and wire wrapping that show up in her intricate gold-pendant necklaces (from $36).