to me it feels as if the education process is ver slow, how do you use this mecanic?

Its a set number of turns based on the "education" level of the skill. For example, if you need to train a fisherman, it will take 4 turns. If you need to train an Elder Statesman it will take 8 turns. The level of the school doesnt matter for timing, only access. Meaning, training a fisherman in a University will still take 4 turns.

If it seems to be taking a while it could be a few things... Petty Criminals and Indentured Servants need to be trained up to to Free Colonists before they become whatever skill you are teaching. It may be they are throwing off your progress. Better to simply train them at indian villages (IS anyway they will turn away PC unless you send them in to become scouts). If you are set on training them up, make sure its for a base profession, no point in spending 8 turns for an Elder Statesman to train a criminal into a servant.

Also, make sure you are not pulling the trainee from the colony during training. For example, removing the one free colonist from the colony to make room for someone else for a turn will cause the timer to reset.

Other than those reasons, it shouldnt take you more than a few turns. Or at least i cant think of any.

Thanks for the post

I did not know that the number of turns are always the same, is there a guide that shows how long which profession needs to be trained ?

You can search online for a full list, I dont recall offhand. Generally, if its a manual labor type job, it requires a schoolhouse. If its an finished good producer or any of the expert planters, its a College. And I believe only Firebrand Preachers and Elder Statesmen require a University. Perhaps Jesuit Missionaries as well.

Go to the "Building Types" menu in the upper right hand corner. Click on the various building types -- Schoolhouse, College and University -- and you'll see what types of units can be trained there. But it won't tell you how many turns it takes to train a particular unit.
Thanks to the other posters for the info on training! Note especially that if you remove the Colonist from the colony you reset the training clock. But you can move the Colonist around within the colony (eg, from working as a Stateman to working as a Carpenter) without resetting the training clock.