How get data from table with NHibernate by where?

Your options are:

• Criteria Queries
• Query Over Queries
• HQL
• Linq2NHibernate
• Native SQL

Personally, I really like the QueryOver API:

var clients = session.QueryOver<Clients>().Where(x => x.Name == "Foobar").List();

If you only need to get an entity by its ID, you can use Get or Load

var client = session.Get<Clients>(5);

If you search for NHibernate tutorials you'll certainly find a lot of information. I've heard good things about the Summer Of NHibernate screencasts, though I personally haven't seen them.