Check out local Law Library

Go to the law library in your county court, and ask the librarian.  I am not sure if you can get a divorce online, but I am sure they have online forms for you to fill and print out.  Probably actual submission has to be done in person.  

If you got your green card for more than 5 years, you can have most of the benefits such as medicaid / food stamp etc.  However, medicaid is different in every state, some state has strict "work requirement" for people your age.  Also consider that your husband might pay you an alimony or give you some asset and those might disqualify you from getting medicaid.  see https://dhs.iowa.gov/

You should talk to a local social worker, I don't know how you might get in touch with one.