Ilija Erceg wrote:How long usually need to prepare for this exam ?
That's very personal and really depends on your experience, learning speed and the time you can spend each day. Here you'll find a very extensive experience of another rancher. And here you'll find another thread about the time to prepare for the exam.
In the OcajpFaq (besides other very useful information) and this thread you'll find an overview of all available resources (study guides, mock exams,...) to thorougly prepare yourself for the OCA certification exam. Another useful resource is the OcajpWallOfFame: you'll find plenty of (links to) experiences from other ranchers. Some of them have described their journey in great detail (even including how much time they spend on each item of their preparation). Other ones shared nothing but the resources they have used. So it can be useful too to determine which resources are useful (and which are not).