Kira kira (きらきら) means sparkling or twinkling: starlight, the sea in the sun, shining eyes.
Stars do not make a noise. Neither does sunlight on the sea. Japanese gives them a sound anyway: きらきら.
What it means
きらきら is light that sparkles: many small points that flash on and off. Stars, snow in the sun, the surface of the sea, jewellery, and eyes that are full of hope all do it.
How to use it
Add しています for something that is sparkling now: きらきらしています. Or put it in front of a verb to say how something shines: きらきら ひかります. In front of a noun it becomes きらきらした: きらきらした め, “sparkling eyes”.
みて ください。 ほしが きらきらして います。
Look. The stars are twinkling.
ほんとうですね。 きれいです。
They really are. It's beautiful.
Close cousins
ぴかぴか is the shine of something clean or brand new: polished shoes, a washed car. ぎらぎら is a hard glare that is almost too strong: the sun in the middle of summer. きらり is a single glint, there and gone. きらきら is the gentle one that keeps twinkling.
In manga and anime
キラキラ is written among little stars around a character who has just appeared looking wonderful, or inside eyes that have seen something they want. It is so common that people talk about “きらきら eyes” as a look.
Can you use it?
Yes, anywhere. It is also a compliment for a person: あのひとは きらきらして います says someone is full of life and doing what they love.