The Catechism Says: 
 
Satan Does Exist 
 
391. "Behind the disobedient choice of our first parents lurks a seductive voice, opposed to God, which makes them fall into death out of envy. [Cf. Gen3:1-5 ; Wis 2:24 .] Scripture and the Church's Tradition see in this being afallen angel, called 'Satan' or the 'devil'. [Cf Jn 8:44 ; Rev 12:9.] The Church teaches that Satan was at first a good angel, made by God: 'The devil and the other demons were indeed created naturally good by God, but they became evil by their own doing. '[Lateran Council IV (1215): DS 800.]" 
 
392. "Scripture speaks of a sin of these angels. [Cf. 2 Pet 2:4 .] This 'fall' consists in the free choice of these created spirits, who radically and irrevocably rejected God and his reign. We find a reflection of that rebellion in the tempter's words to our first parents: 'You will be like God. '[Gen 3:5 .]The devil 'has sinned from the beginning'; he is 'a liar and the father of lies'.[1Jn 3:8 ; Jn 8:44.]" 
 
393. "It is the irrevocable character of their choice, and not a defect in the infinite divine mercy, that makes the angels' sin unforgivable. 'There is no repentance for the angels after their fall, just as there is no repentance for men after death. '[St. John Damascene, Defide orth. 2, 4: PG 94, 877.]" 
 
394. "Scripture witnesses to the disastrous influence of the one Jesus calls 'a murderer from the beginning', who would even try to divert Jesus from the mission received from his Father. [Jn 8:44 ; cf. Mt 4:1-11 .] 'The reason the Son of God appeared was to destroy the works of the devil.'[1Jn 3:8 .] In its consequences the gravest of these works was the mendacious seduction that led man to disobey God." 
 
 
He is only a creature 
 
395. "The power of Satan is, nonetheless, not infinite. He is only a creature, powerful from the fact that he is pure spirit, but still a creature. He cannot prevent the building up of God's reign. Although Satan may act in the world out of hatred for God and his kingdom in Christ Jesus, and although his action may cause grave injuries - of a spiritual nature and, indirectly, even of a physical nature- to each man and to society, the action is permitted by divine providence which with strength and gentleness guides human and cosmic history. It is a great mystery that providence should permit diabolical activity, but 'we knowthat in everything God works for good with those who love him. '[Rom 8:28 .]" 
 
 
Confession Schedule and Preparation 
 
The Four Last Things 
 
Rationalized Sins 
 
Hell 
The 3 Secret Strategies of Satan 
 
1st Secret - All opinions are equal - The modus operandi of today’s mores is to believe that all opinions are equal. Each person’s opinion has the same dignity, deserves the same respect, and is equally as valid as any other opinion.This is a demonic lie.It is a demonic lie because genuine opinion is necessarily related to the virtue of Truth. Objective and fundamental truths are either true or they are not; they cannot be both true and untrue at the same time. Since those issues of faith and morals relate to objective Truth, varying opinions about such issues cannot be equal. In fact, some opinions are silly, some are better than others, and some are just plain wrong.Honest opinion seeks to know the truth and to express it. To know the truth we must know the One who is the Truth: "I am the way, and the truth, and the life" declares Jesus, and through this Truth we shall find freedom—freedom from sin and freedom from the slavery of our limited understandings.  Opinion has value only as it serves to reveal Truth. 
 
2nd Secret - Never judge anyone - Error has no dignity except as a possible motivator to lead us to truth. But if we are not confronted in our error, how can we be motivated to move toward truth?  St. Paul instructs us to judge in his letter 2 Timothy 4:2-4. 
 
We are to judge the teaching of teachers, the opinions of people, the attitudes and behaviors of people. If we don’t, then we allow sin and Satan to exploit the weak and ignorant and vulnerable with his lies.  The sinner needs to know the risk he takes with his soul.  One of the traditional seven Spiritual Works of Mercy is to "Admonish the sinner. 
 
3rd Secret - Never step on toes - We are to be gentle and cordial unless circumstances warrant a more "tough love" approach. But in whatever we do and in however we do it, we are never to compromise truth for the sake of civility or for the sake of popularity or to be accepted by our peers, or for fear of being made fun of or disliked.  Motivation to not offend has caused serious deficiencies on catechesis, preaching, and liturgy.  
 
A Prayer to Saint Michael  
Saint Michael, Archangel, defend us in battle. Be our protection against the wickedness and snares of the Devil.May God rebuke him, we humbly pray;And do thou, O Prince of the Heavenly Host, by the power of God, thrust into hell Satan and all the other evil spirits who prowl about the world seeking the ruin of souls. Amen. 
-- Pope Leo XIII 
 
Other Links: 
 
Saint Michael's Call - MEGA Site