Hey Renata, Today I was looking through the Haitian Creole forum, just making sure no messages fell through the cracks, and I noticed your message. So I will answer it, if you are still interested.
Vodou and Lukumi are very different, but very similar at the same time.
The major 'doctrinal' premises of the two religions are similar, these are a few of the more important ones:
1. God (called Bondyè in Vodou, and Oloddumare in Lukumi) created everything, but is beyond the comprehension of humanity and does not interact with us personally.
2. God has given humanity intermediary powers like angels (orishas in Lukumi, loas or lwè in Vodou) which are identified with natural forces, aspects of life, certain areas, colors and numbers to watch over us, as a whole and as individuals. Everyone, regardless of whether you practice the religion or not has up to 3 guardian orishas. [My primary guardian in Lukumi, for instance, is Ochun, who is the orisha of the rivers, of money, of the emotions, particularly love, and of sex. Her color is yellow and her number is 5. Children of Ochun (no, not literally) have similar traits as Ochun does.
3. Communicating with, respecting and honoring one's ancestors (eggun in Lukumi and zanset yo in Vodou) is important for their spiritual evolution and for our own wellbeing.
4. One can communicate with the orishas, loas and ancestors through possession, divination, etc.
5. The importance of sacrifice and offerings in exchange for something that the practitioner requests. This is seen, not as bribery, but as an interchange of ache (roughly - grace, power, it's also kind of like holy spirit).
Other than that, the two religions diverge significantly. But this shouldn't be surprising - the religions were practiced in different tribes in Africa (what emerged as Vodou by the Ga, Ewe and Fon peoples, and Lukumi by the Yoruba) and in different countries in the New World (the religions interact with different Native American religions as well, which has a different effect on both religions).
First of all, the orishas and loas are different. Ochun in Lukumi and Ezili Freda in Vodou are similar in what they are identified with, but they are not the same, and would greatly resent being treated as such. In traditional Yoruba belief, there are the orishas, forces of good, and the ajoguns, forces of bad, which were both worked with. The orishas, for the goodness of God, and the ajoguns, to leave people alone and not hurt them. In Cuban Lukumi, only the orishas are worked with. In Vodou, there are different categories also. The Rada spirits have been adored since Vodun was practiced in Africa, and are generally more good-natured and calm, while the Petwo spirits are often those of people who died in slave ships going to the new world or in the new world in the bonds of slavery. They are often much more aggressive, and even frightening at times. There are also Congo spirits, whose behavior is between those of the Rada and Petwo rites.
They are also ceremonially and structurally different. Lukumi has several complicated forms of divination, such as diloggun (the cowrie shells), throwing obi (coconut) and opwele (which is used by babalawos [high priests of Lukumi]), while Vodou doesn't have one divination system that is unique to it - Vodouisants often use tarot cards and things like that. The drumming beats for the spirits are different, and the songs are as well. So is the language - Lukumi songs are in Yoruba and Vodou songs in Haitian Creole. Also, in Lukumi, only priests (santeros) and those who the orishas think are ready to become santeros are possessed, and only by their primary orisha. In Vodou, any lwè can possess you...if they choose, of course. The initiations are also different...In Lukumi, you first receive the elekes of the 5 main orishas, which protect you from harm, then the guererros, which are Eleggua, Oggun, Osun and Ochosi, if you want to look them up, and then you receive kariocha and become a priest of your orisha. In Vodou, there are 3 levels of priesthood but no real initiations other than that. In both religions, you don't have to be a priest to participate though. Those are some of the differences, and there are many more.