It happens that you want to use the Ampersand '&' as a character and not as a prefix for variable names. For example you want to put a line like this into a variable:
//SYSLIN DD DSN=&&OBJECT,DISP=(OLD,DELETE)
This can easily be done by using these two lines:
&DSN = &CONCAT & & OBJECT &Q = &STR //SYSLIN DD DSN=&DSN,DISP=(OLD,DELETE)
Variable &DSN is filled with the three character which are concatenated by &CONCAT: '&', '&' and 'OBJECT'. Thus, &DSN is filled with the string &&OBJECT.