Covid regulations to enter Germany from usa

It depends on whether you are vaccinated or not, and on where you are coming from.
As of 15 August, the US was designated a high-risk area by the German health authority. This means that unvaccinated travellers arriving from the US need to have a negative test taken with 72 hours (PCR) or 48 hours (Antigen) of arriving, and also need to quarantine for 10 days (which can be shortened to 5 with a negative test on the 5th day). Fully vaccinated travellers who received vaccinations approved by the EU only need to provide proof of vaccination (only original vaccination documents are accepted, not photos of them). There are also different rules for people who have recently recovered from Covid and have proof of infection.

Here is a description of the rules in English. Note: these rules might will change by the time you travel, so you should check the official site regularly.

(Also, just a tip, but Frankfurt, not Frankfort)

We are on a flight to Frankfurt tonight. A couple of days ago I registered on the German government site and uploaded our proof of vaccination so we are exempt from quarantine. Info here and the process is in English: https://www.germany.info/us-en/service/covid-19/2321562

Note you need to save the PDF produced in the final step. Have it on your smartphone and also print it out. They will NOT email it to you.

Edit: I see I gave you the same link as Azra. As far as return from Rome, or from anywhere, you have to have a test no more than 3 days before travel. There have been several other posts here in the Forum about this recently.