I've seen MANY different ways to query a database...

session.Find
session.CreateCriteria
session.CreateQuery

and also some different ways to make the querystring when parameters are needed

"p.Id = ?"
"p.Id = :IdNumber"
"p.Id = {0}"

what I wanted to know is what is the difference in all this cases.

Ref docs help with this stuff.
For the query types:
- Find is on its way out: Hibernate has already removed it, and future versions of NHibernate probably won't have it. If you use it, be prepared to refactor your code later.
- CreateCriteria uses Criteria, which is most useful if your query is to be generated at run time.
- CreateQuery uses HQL, which is most useful if your query doesn't change (only its parameters do).

For the parameters, see section 10.4.1.4 (of the 3.1 ref docs).

I was looking to the NHibernate documentation... that didn't help much. Here's an idea: why don't you create a documentation like the one in msdn, wich has language filter? that way, you have only one doc for both Hibernate and NHibernate, but where things are different you create both ways and the filter only shows the one that the user desires...
But I must say that the whole forum is great, whenever I have a question or a problem, I know I can find the answer here. And I see that Hibernate's documentation is quite complete (although it doesn't sat anything about "Find" going out... maybe it doesn't even exist in Hibernate?)

Thanks a lot, Tenwit!