1Describes something glittering or sparkling brightly, as light reflects strongly off a surface.
磨いたばかりの窓ガラスがピカピカに光っている。
The freshly cleaned window glass is gleaming.
夕日を受けて、海面がピカピカと輝いていた。
The sea surface glittered in the light of the setting sun.
彼はいつも靴をピカピカに磨いてから出かける。
He always polishes his shoes until they shine before heading out.
2Describes something brand new and shiny, showing no sign of wear; e.g., 'ぴかぴかの新入生' (a shiny, brand-new first-year student).
入学式で、新入生たちはピカピカのランドセルを背負っていた。
At the entrance ceremony, the new students carried brand-new, shiny school backpacks.
買ったばかりのピカピカの車を、近所の人に自慢した。
I showed off my brand-new, shiny car to the neighbors.
このアパートはリフォームされて、部屋がピカピカだ。
This apartment has been renovated, and the rooms are now spotless and shiny.
3Children's usage: describes finishing a plate of food completely, or getting something entirely done.
「野菜を全部食べてピカピカにしたよ！」と子どもが得意げに言った。
"I ate all my vegetables and made my plate all clean!" the child said proudly.
「お片づけできた？」「うん、ピカピカ！」
"Did you finish tidying up?" "Yep, all done!"