Yes. Once you declare the variables in a PLSQL program, you can use it anywhere in the program. See below an example
DECLARE
var VARCHAR2 (100); -- Variable declared
BEGIN
var := 'My name is jack'; -- Assigning a string to the varibale
DBMS_OUTPUT.put_line (var); -- Displaying it.
SELECT 'My name is Mack' INTO var FROM DUAL;
DBMS_OUTPUT.put_line (var);
END;
I hope this helps.