SET SERVEROUTPUT  ON;
DECLARE
    v_salary NUMBER(8); -- i have made a mistake here before
BEGIN
    SELECT salary INTO v_salary FROM employees
    WHERE employee_id = 100;
    DBMS_OUTPUT.PUT_LINE(v_salary);
END;
/ -- this ends your block and allows you to make a new one
DECLARE
    v_salary NUMBER(8);
    v_fname VARCHAR2(20); -- every time you have to be sure that the types of variables match the type of columns from the database.
BEGIN
    SELECT salary, first_name INTO v_salary, v_fname FROM employees  -- same logic but if I select 2 values I also have to put them in 2 diffrent variables
    WHERE employee_id = 100;
    DBMS_OUTPUT.PUT_LINE(v_fname ||' has '||v_salary||' euros.'); -- Example: Victor has 2500 euros. (this will be the output)
END;