KNOW THE  BASIC CONCEPT OF  ELECTRONICS

                
                Current is the number of electrons flowing through something. Current is usually measured in Amperes (or amps). One amp is defined as one coulomb (6.28X10¹⁸ electrons!) of electrons flowing per second. If you want to use the water analogy, think of this as the volume of water flowing through a pipe. Voltage is the difference in electrical potential between two points. Positive voltage is usually defined as the absence of electrons; negative voltages have an excess of electrons. Ground is defined as totally neutral, with an even amount of protons and electrons. Think of voltage as the amount of pressure the water in the pipe is under.

RESISTANCE AND ITS UNIT: 
Resistance is measured in Ohms. At a given voltage, the resistance determines the amount of current that can flow, according to Ohm’s law. Compare the resistance to the size of the pipe the water is flowing through. The larger the pipe (Lower resistance), the more water (current) can flow through.

 The Omh's law is

                              I = E/R 

Where::
I = Current in amps.
E = Voltage in Volts.
R = Resistance in Ohms.

RESISTORS:

                    Resistors are arguably the most commonly used components in all of electronics.  Without resistors, circuits would fry, there would be no analog electronics, life would be bad for electronics in general. Resistors come in a few different wattage ratings; common power ratings are 1/8, 1/4, 1/2, 1, and 2 watts. If a circuit doesn't specify which wattage rating to use, I generally use 1/4 watt carbon film resistors. Larger watt resistors are physically larger and able to dissipate more heat.
 
Capacitors:

Capacitors are like miniature batteries. They store small electrical charges, can discharge them rapidly, and are very frequently used in electronics. However, they are far more efficient than batteries, but have a fraction of the energy storing ability. Capacitors are often referred to as caps, since people get sick of writing out the word.‘capacitor’. Capacitors are measured in Farads. One Farad is equal to one Coulomb of charge at one Volt of potential. Again, one amp is equal toCoulombofelectrons per second. One Farad of capacitance is a huge amount, and can usually only be found in expensive gold foil capacitors, such as thelarge black one shown at left .Capacitors come in two general flavors, polarized and non-polarized. Polarized capacitors have a positive and negative terminal, and you had better pay attention that you stick it in the circuit right, because certain
capacitors can explode when connected backwards at their rated voltage. 

Diodes and Transistors:

Diodes and transistors are generally comprised of two types of silicon; for lack of a better name, we’ll call them type P and type N silicon, and  we are not going into molecular details, this is a crash course, after all....P means that it is positively charged, N is negatively charged. When combined together, these two types of silicon make diodes, transistors, and all that nifty stuff that allows computers to work...Transistors are also a whole lot smaller and cheaper than their predecessor...the vacuum tube. Diodes have a single junction, which is where the P silicon and N silicon touch. When the P silicon is connected to a positive voltage greater than what is called a threshold voltage (0.7 for silicon, 0.3 for germanium), the diode conducts almost like a closed switch and is called forward biased. If you connect the P silicon to a negative voltage, then it is considered reverse biased and will not conduct electricity. The P silicon in a diode is called the Anode, the N silicon is the Cathode.

Transistors:
                     Bipolar transistors come in a variety of packages and types. They are called Bipolar because they have
two junctions, and can be divided into two types: PNP and NPN. NPN means that it has two negative silicon plates sandwiching a positive silicon plate. They can almost be thought of as two diodes that were squished with the P or N sides together.
                    Almost every transistor has three pins  a collector, base, and emitter.  The emitter pin is designated by a small arrow pointing in (towards the center of the circle) or out (away from the center). The easy way to remember if a transistor is a PNP or an NPN by looking at a schematic is to see if the arrow is pointing in or out. 

INTEGRATED CIRCUITS:

      Integrated circuits (or IC's) are those funny little black boxes with little metal pins sticking out of them . The ones that are rectangular shaped and have pins on opposite sides are called DIPs (Dual Inline Pins). SIP (Single Inline Pins) IC's are less common, but do exist. You will  love IC's, as they will save you a lot of time since they contain tiny circuits that will prevent you from having to solder together lots of transistors and resistors to get a digital logic gate.