Review the two types of straight cuts you will make when cutting large boards down to smaller ones: rip cuts and crosscuts.
You'll reduce a lot of large pieces of wood to smaller ones when you build projects. The straight cuts you make are either rip cuts or crosscuts.
A rip cut reduces the width of a piece of stock. On a board, it's a cut along the length in the direction of the grain. On plywood and other sheet goods, it's a cut parallel to the sheet's long side, no matter the direction of the grain. Ripping stock to width is usually the first machining step in building a project.
After stock has been ripped to the width desired, it's cut to length with a crosscut. This is done across (perpendicular to) the board's grain or in the narrow dimension of plywood and other sheet goods. Parts of the same length should be sawed at the same time (especially with power saws) using a stop. A stop is a piece of wood clamped in place so the stock being cut won't move beyond the required length. Using a stop eliminates remeasuring.
The tiny splinters, fractures, and rough edges caused by a blade exiting the wood is called tearout. It is especially noticeable when ripping plywood with a power saw.
To avoid tearout when ripping with a portable circular saw, place the best face of the workpiece down and away from the blade. Then any tearout will be on the bad side of the sheet, which will probably be hidden. For that reason, draw all cut lines on the bad face.
When ripping with a table saw, do just the opposite. Draw cut lines on the best face and place that side up on the table.