Well, you'd use System.Data.OleDb namespace to interact with data stored in the .mdb or .accdb format. Look at MSDN documentation on the namespace. You'll need to know about OleDbConnection, OleDbCommand, and depending on your purposes, DataAdaptor & DataSet/DataTables or DataReader.
But... if you're going to all the trouble of programming in C#, why even bother with Access database? Use SQLite or SQL Compact Edition and distribute that with your C# application so you don't have to worry about version or whether the Windows has the right program installed.