they will leave it with a note and some info like tracking #, name and signature and if you have somewhere they can leave it where its not out in the open. I have my BBQ grill out in front of my house with a cover on it and UPS and FEDEX usually leave my packages under the cover if no one is home when they deliver packages
Been through this a million times with Verizon phone shipments. Always left a note with my name, tracking number, and signature and said "OK TO LEAVE ON PORCH" and they have always left it.
Worst case you can go tonight to the FedEx location and pick it up