Vendor v = new Vendor();
v.VendorName = "Oracle";

Product p = new Product();
p.Vendor = v;
p.ProductSKU = "ORDB10G";
p.ProductName = "Oracle 10g";
v.Products.Add(p);

p = new Product();
p.Vendor = v;
p.ProductSKU = "ORSVC10";
p.ProductName = "Oracle Services For Java 10";
v.Products.Add(p);

v.Persist();

Here's an example showing how to load all instances of a given entity, using a static entity method:

List<Customer> custs = Customer.LoadAll();

Two more examples showing ways to load entities using a template (query-by-example):

Product pt = new Product();
pt.ProductSKU = "VS2005PRO";
List<Product> list1 = Product.LoadByTemplate(pt);

Vendor vt = new Vendor();
vt.VendorName = "Microsoft";
TemplateLoader<Vendor> ldr = new TemplateLoader<Vendor>(vt);
List<Vendor> list2 = ldr.Load();

Loading one or many entities by key:

Order o = Order.LoadByKey("123");

List<Order> orders = Order.LoadByKey(new string[] { "123", "456" });

Slipjig can set up a data command to call any arbitrary stored procedure.  It also provides a method to set all the parameter values in one shot.  This is more of an ad-hoc convenience thing than anything else; in particular, SetParamValues() is not type-safe and wouldn't be part of everyday usage.  Here's a sample calling a stored proc that takes an instance of every data type:

using (IDbSql db = (IDbSql)DbFactory.GetDB("Test")) {
    IDbCommand cmd = db.GetStoredProcCommand("usp_test");
    db.SetParamValues(cmd, 1, 1, 1, 1, "a", "a", "a", "a", "a", "a", "a", "2006-02-24", "2006-02-24", 0, new byte[] {}, new byte[] {}, new byte[] {}, new byte[] {}, 0m, 0m, 0, 0, 0, Guid.NewGuid(), 0);

    int recs = db.ExecuteNonQuery(cmd);
}