A solderless breadboard lets you build a circuit without soldering: metal clips hidden beneath the surface join specific groups of holes together, so plugging a part into the right holes wires it into the circuit.
Two power rails run the length of each edge (red for positive, blue for ground). The main field is terminal strips: short rows of five holes wired together. A center divider splits the board so a chip can straddle it with a leg on each side.
Every highlighted hole is wired to the one you clicked. They are a single connection: one node of your circuit.
Anatomy diagram and build photo from the Adafruit Breadboards for Beginners guide, used with permission.