What goes in the top box?
The conclusion of an argument is the claim the argument supports (or opposes) overall. In other words, all the other claims in the argument somehow support (or oppose) this conclusion, and the argument does not use the conclusion to directly support (or oppose) any other claim. This does not mean that the conclusion—in the sense relevant here—is always what the author of the passage believes. Sometimes the conclusion is a claim that the author of an argument disagrees with (or doesn't take a side on).
For a concrete example where an author does not necessarily believe the conclusion of the argument, consider this text:
People sometimes argue that medical researchers should not pursue enhancement technology because such technology goes beyond the purpose of medicine. But consider that many medical treatments already accepted as serving the purposes of medicine are not intended to cure illness or reduce discomfort: Plastic surgery and contraceptive medication are just two examples.
The conclusion is that medical researchers should pursue enhancement technology. Does the author believe it? Maybe. But maybe not. You could make an informed guess, but judging from this passage alone, you can’t really be sure. Still, you can be confident that the author doesn't think that Claims 2.3 and 2.4 in this analysis jointly support the conclusion: