A schematic is a map of connections, not of the physical parts. Symbols stand for components and lines for the wires that join them. Once you can read one, you can build from a published design, repair a radio from its manual, or work out how a circuit behaves without ever seeing it.
Connections, not appearance
A schematic keeps the connections and throws away looks, size and wire length.
Draw the same circuit as a photograph and as a schematic and only the connections carry over. A schematic is laid out for readability, so a wire that looks long on paper may be a short link on the board, and parts that sit side by side on the page may be far apart in the box.
Reading one
Follow the wires from the + side of the source, through each part, back to the − side.
Start at the source and follow the path of current, one part at a time. At each component, ask what it does to the signal or the current. Where a wire splits into branches, the dot shows that they are joined.
Each part carries a reference designator and often a value. Letters follow convention:
Letter
Part
Letter
Part
R
resistor
Q
transistor
C
capacitor
U
integrated circuit
L
inductor
T
transformer
D
diode, LED
S
switch
F
fuse
Y
crystal
Values may be written with the prefix in place of the decimal point to avoid a lost dot: 4k7 is 4.7 kΩ and 2n2 is 2.2 nF.
The symbols
Symbols vary a little between countries and eras. The US style used here draws the resistor as a zigzag; the international style uses a box. Some diagrams draw ground as the three-line symbol, others as a bar with slanted hatch lines. The idea is the same.
In practice
Many schematics repeat the power connections by labels (+12 V, GND) rather than drawing every wire, so a symbol meaning "ground" appears all over the page.
A block diagram shows stages and signal flow; a schematic shows the components inside each stage. Read the block diagram first to know where you are.
Before building, check that every pin is accounted for. Symbols for transistors and ICs show which lead is which.