Can I use same Apple ID for my iPad as well as iPhone

Absolutely. An Apple ID is intended for use by exactly one person, regardless of age. It should never be shared. It is used on all devices used by that one person.

You need to log in with your Apple ID, not create an Apple ID during setup.

When I setting up on my iPad same Apple ID as my phone it says ID already used.

poonam252 wrote:

When I setting up on my iPad

What might this mean exactly?

Set up your iPhone, iPad, or iPod touch - Apple Support