I have used Radzen (the original) and build some applications, it is nice to use Radzen out of the box but sometime I need to run Stored Procedures to fecth data or to store complex data in several tables.
So in old Radzen I know how it works but in Radzen Blazer Studio it works fine if I don't need to pass parameters.
If its a simple usp with parameters you just select the SQL usp when creating/updating the datasource and RBS will automatically create the model and service methods to access the usp.
You need to inject the data service that was generated for your data source. Then you can invoke its methods. You can copy it from another page which already performs data access. It is a property that should look something like this:
[Inject]
public NorthwindService NorthwindService { get; set; }