To return a string that comprises the left-most n characters of x$.
n must be within the range of 0 to 255. If n is greater than LEN(x$), the entire string (x$) will be returned. If n equals zero, the null string (length zero) is returned (see the MID$ and RIGHT$ substring functions).
10 A$="BASIC" 20 B$=LEFT$(A$, 3) 30 PRINT B$ RUN BAS
The left-most three letters of the string "BASIC" are printed on the screen.