Dates
Recall that there are only two types of variables: numeric and character.
Dates are stored as a numeric value.
The informat tells SAS how to read the raw character values "012366".
What is stored is the number of days since January 1, 1960.
For example:

 DATA POINTER;  
   INPUT @1  ID       3.  
         @13 CharDOB  $6.  
         @13 DOB      MMDDYY6.;
  
DATALINES;  
101 M 26 68 012366  
102 M 32 78 031460  
103 F 45 62 112647  
104 F 22 66 080170  
;  
PROC PRINT DATA=POINTER;  
   TITLE 'Example 6, modified';  
RUN;

Note that the same data was read more than once (for another example of this, see example 8 in chapter 1).
The code produces the following output:

Example 6, modified
  
OBS     ID    CHARDOB      DOB
  
 1     101    012366      2214  
 2     102    031460        73  
 3     103    112647     -4419  
 4     104    080170      3865

Important Notes:
Dates are stored as the number of days since 1960.
To make the internal numeric value print correctly, use the FORMAT statement.