The slide rule side of the E6B computer is used to calculate time, speed and distance. The scales on the outer circle and the first scale on the inner disk are identical. Also on the inner disk is an additional scale that represents hours corresponding to the number of minutes on the first scale. Think of the edge of the inner disk as representing the word "per", such as "miles per hour", gallons per minute, etc.
To calculate any rate, simply place the black triangle on the inner disk opposite the number on the outer scale that represents the value that changes with time, such as miles per hour and gallons per hour. Then, opposite the number of minutes on the inner disk, you can read the result. Naturally, you need to provide the zero or decimal point if appropriate by first estimating an answer to comply with the TLAR (That Looks About Right) rule.
To compute True Air Speed, use the small window and align the temperature opposite the altitude and read the True Air Speed on the outer scale opposite the Calibrated Air Speed on the inner disk.