You can use splits like Jake said but not plain old fire wood. You want dry seasoned oak, cherry, hickory, mesquite.....you get the picture any hard wood used in a normal smoker.
just as a suggestion if you start with a full chimney of good charcoal. Get them good and lit then you can put 3 or 4 splits on them. Once those are good and lit, ie burning clean then you can put your desired protein off to the side of the heat for smoking or you can grill right over the fire and coals.
I would also you put a temp probe in about 4 inches away from the meat and that will tell you what how to adjust the fire, location of meat...etc
bottom line you have a sweet smoker there!!! Some of the best BBQ in the world is made on pits like yours! There is a place famous for smoked whole hogs & they have a wood fire out side and just shovel the hot wood coals around the edge of the brick and they have the hog in the center.......the natural wood coals make out smoked golden goodness!
Looks like live coals to fire it with, is there a spot close that may have been used to make a fire? like the others said small splits as the meat is over the top of it, it will have to seal good to keep the flare ups under control , with live coals that's a lot easier to do than with wood that's not caught on fire yet.
Thank y'all for the replies! I have put a couple of logs in it to see how things went before, didn't let much if any smoke out of the lid. Would it be a good idea to replace the expanded metal grate? I hate to lose 50 years of seasoning on it, but without knowing what the previous owner put in there... other than beer cans. Looking forward to trying something in it. The small brinkmann I have won't hold near as much!