A datasheet is typically divided in the following sections:
The first page is usually a summary of the part’s function and features. Here you can quickly find a description of the part's functionality, the basic specifications and sometimes a functional block diagram that shows the internal functions of the part.
A pinout shows the part’s pins, their functions, and where they are physically located on the part for various packages the part might be available in. Note the special marks on the part for determining where pin 1 (typically a point on the package) is and how the pins are numbered. You'll find some acronyms here: VCC is the supply voltage (commonly 5V or 3.3V), CLK is clock, CLR is clear, OE is output enable, etc. These acronyms should be spelled out later in the datasheet, but if not, try Google or Wikipedia.
These data are detailed tables of electrical specifications. These will often list the absolute maximum ratings a part can withstand before being damaged. Never exceed these or you'll be replacing a possibly expensive part!
Some parts will have one or more graphs showing the part’s performance vs. various criteria (supply voltage, temperature, etc.). Check out for "safe zones" where reliable operation is guaranteed!
Some components may show one or more truth tables. Truth tables show how changing the inputs to a part will affect its output. Each line has all the part's inputs set to specific states, and the resulting output of the part. "H" means that input is a logical high (usually VCC), "L" means a logical low (usually GND), "X" means the chip doesn't care what the input is (could be H or L), and an arrow means that that you should change the state of that pin from L to H or H to L depending on the arrow direction. This is called "clocking" an input, and many chips rely on this for proper operation:
Timing diagrams show how data should be sent to and received from the part, and what speed it should be sent/received. These are typically laid out with various inputs and outputs as horizontal lines, showing the logic transitions that happen to those lines over time. If the trace dips down, that's a L input or output. If the line rises higher, that's a H input our output. Timing specifications are laid out as arrows between transitions (names are referenced back to timing numbers in the electrical specs), and vertical bars or arrows will link related transitions.
Most components present this section which help you showing typical circuits where you can find the component.
At the end of many datasheets you can find packaging information, which provides accurate dimensions of the packages a part is available in.