This means that all silicone diodes have a voltage drop of 0.7v. This fixed voltage drop is usefull in many functions. A PN junction diode allows current to flow in one direction, while preventing current flow from the other, depending on the bias. The next step is learning to bias the diode. Forward bias allows current to flow throught the diode.
Reverse bias prevents current to flow through a diode.
Both forms of the Bias are useful in a circuit. When a diode is placed in a circuit so that the Anode, or positive end, is connected to the positive terminal of the battery, and the Cathode , or negative end, is connected to the negatve terminal, the diode is considered to have a forward bias . This causeds current to flow through the diode with little resistance. This happens because the Junction where the P and N semiconductors meet acts as an insulator during reverse bias. Therefore, current cannot flow.