C# When to use capital letter for names?

PascalCasing for class names and method names:

public class ClientActivity
{
  public void ClearStatistics()
  {
    //...
  }
  public void CalculateStatistics()
  {
    //...
  }
}

Do use camelCasing for method arguments and local variables

public class UserLog
{
  public void Add(LogEvent logEvent)
  {
    int itemCount = logEvent.Items.Count;
    // ...
  }
}