Cool, thanks.
Few more: Can humans be turned into demons and do some demons escape hell? Is it possible for them to manifest on earth?
No, humans can't become angels or demons.
Matthew 25:41 mentions the eternal fire prepared for the Devil and his angels. In the Orthodox view, God is the light of heaven and the fire of 'hell' (even though this word is actually a misnomer- the proper terms which tend to be translated into the word 'hell' are hades and gehenna), how one experiences this is based on their disposition toward God. There are people who pray for the repentance of all creation (including angels), but this actuality is something that only God knows.
Are you asking whether or not it is possible for angels and demons to manifest on earth? Angels are the bodiless powers of heaven. People have certainly had experiences with both. It is not advised to seek out such experiences, however.
ETA: We do believe in guardian angels. Here is an article about the Church's belief in guardian angels:
http://www.antiochian.org/node/18443
Also, as part of the daily prayers, there is a prayer to your guardian angel. We also have prayers to our patron saints, and mine happens to be the Archangel Michael.
A PRAYER TO YOUR GUARDIAN ANGEL O Angel of Christ, holy guardian and protector of my soul and body, forgive me everything wherein I have offended thee every day of my life, and protect me from all influence and temptation of the evil one. May I nevermore anger God by any sin. Pray for me to the Lord, that He may make me worthy of the grace of the All-holy Trinity, and of the Most Blessed Theotokos, and of all the Saints. Amen.
ETA again: Here are some other articles about Orthodox Christian beliefs regarding angels and fallen angels.
At the Threshold of Fiery Gehenna: Teachings of the Orthodox Church concerning Evil Spirits and God's judgment over them
http://www.fatheralexander.org/booklets/english/threshold_hell.htm
Angels: Blessed Messengers of God
http://www.fatheralexander.org/booklets/english/angels.htm
Counterfeit Angels
http://www.fatheralexander.org/booklets/english/angels_e2.htm