The INPUT statement reads raw data using column input.
From 'The little SAS BOOK':
'After the INPUT keyword, list the first variable's name. If the variable is character, leave a space; then place a $. After the $, or variable name if it is numeric, leave a space; then list the column or range of columns for that variable.'
That is, 1-4 means extract the first column to the fourth column and assign it to ID as a numeric value. $ 21 means extract the 21st column and assign it to Sex as a character value.

I am also a new learn and my English is poor. Hope it helps you.

Thanks a ton!