Best way to manage and serialize objects in C#

Best way to manage and serialize objects in C#

I'm writing one C# application to improve my basic understanding of .NET,
and I would like to know what is the best way to do what I need for. Best
means for me: simple to code and efficient to use.
My application have to work with objects (of the same type, eg. AAA), and
it creates different collections of them... so I'll have a Collection of
Collections of AAA.
My main needs are: - to work with this main collection in memory and to
persist (serialize) it on disk; - to deserialize from disk into memory;
Another need can be: - to "query" its data (eg. "give me all the
collection in which contained objects has a specified value of a field").
Thank you for you indications.