In a flowchart proof, statements and conclusions are connected with arrows.
In terms of mathematics, a statement is simply any sentence in which it can be verifiably true or false. A statement cannot be a subjective opinion. It must be an objective fact and there must not be any ambiguity involved. A conclusion is also a statement that derives from the first statement made.
As an example, you can have the simple argument "if it rains, then it gets wet outside". So the box on the left would be "it rains" and the box on the right would be "it gets wet outside". An arrow connecting the two shows the logical flow of how the argument is set up.
See the diagram below.
Side note: the box on the left is also considered the antecedent because it comes before the conclusion.