note that single quotes ARE needed here:

Enter value for job_ttl: 'Manager'
old   3: where   job_title = &job_ttl
new   3: where   job_title = 'Manager'

    SALARY                                                                      
----------                                                                      
      2975                                                                      
      2850                                                                      
      2450                                                                      

DO NOT need quotes here:

Enter value for qtd_job_ttl: Manager
old   3: where   job_title = '&qtd_job_ttl'
new   3: where   job_title = 'Manager'

    SALARY                                                                      
----------                                                                      
      2975                                                                      
      2850                                                                      
      2450                                                                      

Enter value for oink: oops
Moo oops

looks like HAVE to put a name after an '&'
character:

SP2-0317: expected symbol name is missing
how about this? &

give salaries for those with the desired job_title
(quotes required!):

Enter value for job_ttl: 'Sales'
old   3: where  job_title = &job_ttl
new   3: where  job_title = 'Sales'

    SALARY                                                                      
----------                                                                      
      1600                                                                      
      1250                                                                      
      1250                                                                      
      1500                                                                      

give last names for those with the desired job_title
(quotes required!):

Enter value for job_ttl: 'Sales'
old   3: where  job_title = &job_ttl
new   3: where  job_title = 'Sales'

EMPL_LAST_NAME                                                                  
---------------                                                                 
Michaels                                                                        
Ward                                                                            
Martin                                                                          
Turner                                                                          

needs BOTH join and nesting

I want the manager's name AND the clerk's name
AND the salary for clerk(s) making the
highest salary

MANAGER         CLERK               SALARY                                      
--------------- --------------- ----------                                      
Raimi           Miller                1300                                      

employee last names and salaries of those who work
in Chicago, using subselect:

EMPL_LAST_NAME      SALARY                                                      
--------------- ----------                                                      
Blake                 2850                                                      
Michaels              1600                                                      
Ward                  1250                                                      
Martin                1250                                                      
Turner                1500                                                      
James                  950                                                      

6 rows selected.

employee last names and salaries of those who work
in Chicago, using join:

EMPL_LAST_NAME      SALARY                                                      
--------------- ----------                                                      
Blake                 2850                                                      
Michaels              1600                                                      
Ward                  1250                                                      
Martin                1250                                                      
Turner                1500                                                      
James                  950                                                      

6 rows selected.

dept names and locations of departments that have
at least one employee hired before June 1, 1991,
using nesting:

DEPT_NAME       DEPT_LOC                                                        
--------------- ---------------                                                 
Research        Dallas                                                          
Sales           Chicago                                                         

dept names and locations of departments that have
at least one employee hired before June 1, 1991,
using join:
(make sure you understand WHY more rows are projected here)

DEPT_NAME       DEPT_LOC                                                        
--------------- ---------------                                                 
Research        Dallas                                                          
Research        Dallas                                                          
Sales           Chicago                                                         
Sales           Chicago                                                         
Sales           Chicago