Redistributing VistaDB with your product is very easy - just place the appropriate runtime Dll(s) in the same directory as your executable (or in the bin folder of your web project). Typically, you will also need to register the VistaDB Engine with ADO.NET so that it can be found when using Entity Framework or Typed DataSets. This is done through the configuration file for the application.
Refer to VistaDB documentation for full details on Deploying your Application. And if your application uses Entity Framework see Using VistaDB with Entity Framework - Registering the Provider for additional configuration necessary to register the EF provider with your application.