Help in procedures triggers and basic SQL functions

Personal the question is this:

Develop 4 screens of cadastros , Usuários , Cidades , UF and Produtos . For each screen you should have the procedures of insert , updade and delete . You should also have the validation triggers and key generation functions of each table.

I've already done the tables:

CREATE TABLE TBUSUARIO 
( 
        CODIGO      NUMBER
    ,   NOME        VARCHAR2(50)
    ,   SENHA       VARCHAR(6)
    ,   SITUACAO    VARCHAR(1)
    ,   PRIMARY KEY (COD_USER)
);

CREATE TABLE TBCIDADES 
(  
        CODIGO      NUMBER
    ,   NOME        VARCHAR2(30)
    ,   UF          VARCHAR2(2)
    ,   COD_IBGE    NUMBER
    ,   PRIMARY KEY (COD_CID)
);

CREATE TABLE TBUF 
( 
        COD_UF      NUMBER
    ,   NOME        VARCHAR2(30)
    ,   SIGLA       VARCHAR2(2)
    ,   PRIMARY KEY (COD_UF)
);

CREATE TABLE TBPRODUTOS
( 
        COD_PROD    NUMBER
    ,   NOME        VARCHAR2(30)
    ,   QTDE        NUMBER
    ,   PRECO       (14,2)
    ,   PRIMARY KEY (COD_PROD)
);

The procedure I did was as follows:

CREATE OR REPLACE PROCEDURE PCNOVOLOGIN
(
        NNOME   IN VARCHAR
    ,   NSENHA  IN VARCHAR       
) IS
BEGIN  
    INSERT INTO TBUSUARIO(NOME, SENHA) VALUES(NNOME, NSENHA);

    IF NNOME IS NOT NULL AND NSENHA IS NOT NULL
        ALTER TABLE TBUSUARIO ADD SITUACAO = 'A' END IF;
END PCNOVOLOGIN;

Am I on the right track?

How do I do the procedure of update and delete ? (putting the USUARIO table in question). One more, how do I function to generate sequential table code?

I'm very inexperienced in sql , I need help from you ! grateful.