I am new to .NET and have heard about several different ways of querying a SQL Server databse such as ADO.NET and the entity framework.
Can anyone give me some advis
NHibernate is the way to go. See http://nhforge.org and http://sf.net/projects/nhibernate for more information.
The main difference between Entity Framework and NHibernate is that Entity Framework is only for Microsoft SQL Server (Oracle is kind of supported, but support is not ideal). NHibernate supports many many many databases.