Incorrect spelling, explanation: this spelling, beachs is incorrect, and the correct one is beaches, as the singular form beach ends with ch sound, which means we have to add vowel e before plural-forming s. Therefore the plural form of beach is beaches, not beachs.

Correct spelling, explanation: beaches is the correct plural form of beach, due to a simple rule, that if a noun ends with h, ch, s, sh, or ss sound, then we have to add a vowel e before adding s in order to create a plural form. Therefore beachs is a mistake and beaches is the correct form.

Definition of beaches:
noun, the plural form of beach, seaside, or any other shore sand/rock territories
I love Italian beaches.
Beaches bore me. It’s just lying on the sand in the sun.