How do I connect my hp office jet 6100 printer to my I pad

If you cannot find AirPrint update for the printer firmware.. and it is only USB printer.. it might still be possible to print from iPad using special software and plugging the printer into a computer (or some routers also support this).

eg Printopia is the best known.

https://thesweetsetup.com/apps/our-favorite-airprint-enabler/

I am not 100% sure what this software does but HP does seem to offer it to support network printing.

https://support.hp.com/us-en/drivers/selfservice/swdetails/hp-officejet-6100-eprinter-series-h611/4322969/model/4323174/swItemId/lj-96049-9

I don't think you can. That printer isn't on the list of AirPrint compatible models.

See if the following HP Support article can help:

• Easily print from your smartphone or tablet - HP Support