Someone called to offer to buy our home that wasn't on the market?

Today, a known realtor in our town called to say she had a buyer that was interested in buying our rental property. This was completely out of the blue so didn't say much but that I would speak with my husband and get back to her. This is a property that my father owned and we got from him although it is not the house we grew up in. The house is appraised at about $53,310 2 yrs ago and real estate around here is getting beter. The house needs quite a bit of work still, but was recently releveled, has had electric, plumbing, a/c install, few walls, replaced. The $53,310 was the appraisal when we bought the house. Oh, by the way, it is a 100 yr. old 3bdrm. 2 bath.(although one bathroom has had demo work done) A nice neighborhood in the orignal part of town. We were planning to fix up the house( didn't expect it to be so much) and rent it out and possibly sell in a few years. I don't know how this works, do they make an offer first or do I tell them what I want for the house?