old ipad

Rather limited information. Do you intend to create a new AppleID to use with this iPad - or use an existing AppleID?

If the iPad has already been activated - and is already associated with an existing AppleID that you do not wish to use - be sure to follow this process before proceeding:

https://support.apple.com/en-gb/HT201351

If intending to use a new AppleID with this iPad, follow this:

https://support.apple.com/en-gb/HT204316

Otherwise, if using an established AppleID, simply enter this username/password during the device activation process.

I hope your find this to be helpful in covering all the likely permutations of what you’re attempting to achieve - and provides you with the solution you need.