I want to Marry a lady who ls in Haiti. She is coming to America on a Visa. How can we legally marry?

If she has the proper ID required to get a marriage licene in your state, yes you can marry. That does not change her legal status automatically, so she will have to apply for a change in visa status and latter for citizenship.
No change is for sure, but you can marry.

I want to Marry a lady who ls in Haiti. She is coming to America on a Visa. How can we legally marry?

You need to follow standard procedures like all Americans. She must provide a proper photo ID, passport is good.

To get married is one thing but it does not automatically give her citizenship. You have to follow immigration procedures so she can become lawful permanent resident.

Make sure she has been in US longer than 60 days before you get married. Important, do not get married as soon as she arrives. Currently USCIS denied applications submitted by those who entered US on visitor's visas but married to US citizens within 60 days. If her I-94 is valid for a shorter period of time, or has No AOS, No COS No EOS stamped on it, she has to return to her home country and you must file spouse visa for her.

No AOS, No COS No EOS means cannot adjust status, cannot change status and cannot extend status.... Good luck.