Why Ir De Compras?

The word compra is a noun that means "purchase", "an act of buying". Ir de compras means "to go shopping", "to go on a shopping tour". It's in the plural because you'll probably shop for several items, and also because that's just how the phrase is used (it's a fixed idiom).

Is ir de Compras singular or plural?

It's not the second person singular form of the verb comprar, it's the plural form of the noun compra (purchase), though that ultimately derives from the been comprar.

Is ir de Compras a verb?

"Ir de compras" is an intransitive verb phrase which is often translated as "to go shopping", and "ir a comprar" is a transitive verb phrase which is often translated as "to go to buy".