How different were the lives of people in central Africa (Congo) in 1800 AD from the people of Central Africa in 0 AD

Central Africa is a pretty big umbrella. Even "Congo" (which one? Where in the Congo basin?) is a tough thing. But we can hazard a few considerations, despite Jean-Paul Chretien's long ramble about the difficulty in The Great Lakes of Africa. For argument's sake I'll assume you're talking about the forest edge of the central eastern DRC.

First, and perhaps most immediately notable, the 1800 communities will have a far wider range of foodstuffs. Between 0 and 1800, not only did the banana transmit from the Indian Ocean, but the entire set of New World cultivars (that could handle tropical environments) would have come across. That includes maize and manioc/cassava, really exceptional sources of carbs and calories. A population rise would likely be the case in this region, although within a generation or two they'd be dealing with the issue of slave raiding from the eastern coast of Africa (mostly via Zanzibar).

Another distinction would be the presence of firearms. It's hard to be certain how widespread their ownership was, but trade weapons coming via Angola and Tanganyika were definitely known but not common by 1800, as the nearby Lunda Empire fell rapidly to the gun-armed forces of Chokwe later in the century. The presence of people from far away at the coast for trade would be generally known at least to the elites, if only in an abstract sense, but a many-hands trade is almost impossible to deny.

But ironworking existed at both times, the culture, religion, etc., of the core populations differed but only evolutionarily (and the nature of that is not clear--we see it in pottery but with so little extended work it's much harder to track in terms of ideas). I'll see what's out there, but Belgian and French studies tended to be ethnographical, ahistorical, and when archaeological were descriptive more than analytical. This is one problem that Vansina, whom I mention below, encountered. We also don't have a good idea of the monumental works that people constructed, because these tended to be destroyed or lost--even utilitarian ones, like terraced agriculture.

It's hard to say what about the core "Bantu toolkit" (food, animals, etc) might be different in that area from 0 to 1800. Assuming that they had the ability to alter their landscapes in the same degree (and it was significant two thousand years ago--make no mistake, per Chris Ehret's An African Classical Age) then periodic transhumance would have given way somewhat to more long-term maintenance of land. The presence of disease-resistant breeds of sanga cattle--such as Ankole, which are usually further north--would also be notable, but archaeologists argue over when and where such cattle became viable to keep.

Depending on where you were, in 1800 you might be part of the Luba Kingdom or tributary to it (if far to the east). The specifics of that kingdom are easy enough to find (and covered in Tom Reefe's The Rainbow and the Kings in 1981) but it's hard to say how novel the formation was, because we don't have clear descriptions of state formations as far back as the first century CE. That doesn't mean they weren't there.

Now, if you were somewhere else in the purported "Central African" region, like Rwanda, or Angola, maybe Cameroon, your experiences and lifestyle might be quite different at each time or just in general. But this is one attempt to lay out some general points.

This region, and some of the issues involved in studying them, were the subject of the germinal Kingdoms of the Savanna by Jan Vansina in 1966, which really helped to kick-start study of the region and in many ways helped to shape African History as a self-critical discipline. There are other works too, to be sure, but those are some to start with.