Implement windows service in .NET 6.0

I have created a window service by using
https://learn.microsoft.com/en-us/dotnet/framework/windows-services/walkthrough-creating-a-windows-service-application-in-the-component-designer

Here they have used some win32 calls I do not understand that please can u explain why they used and what the functionality of those win32 calls for service

using System.Runtime.InteropServices;

public enum ServiceState
{
SERVICE_STOPPED = 0x00000001,
SERVICE_START_PENDING = 0x00000002,
SERVICE_STOP_PENDING = 0x00000003,
SERVICE_RUNNING = 0x00000004,
SERVICE_CONTINUE_PENDING = 0x00000005,
SERVICE_PAUSE_PENDING = 0x00000006,
SERVICE_PAUSED = 0x00000007,
}

[StructLayout(LayoutKind.Sequential)]
public struct ServiceStatus
{
public int dwServiceType;
public ServiceState dwCurrentState;
public int dwControlsAccepted;
public int dwWin32ExitCode;
public int dwServiceSpecificExitCode;
public int dwCheckPoint;
public int dwWaitHint;
};
[DllImport("advapi32.dll", SetLastError = true)]
private static extern bool SetServiceStatus(System.IntPtr handle, ref ServiceStatus serviceStatus);

// Update the service state to Start Pending.
ServiceStatus serviceStatus = new ServiceStatus();
serviceStatus.dwCurrentState = ServiceState.SERVICE_START_PENDING;
serviceStatus.dwWaitHint = 100000;
SetServiceStatus(this.ServiceHandle, ref serviceStatus);

// Update the service state to Running.
serviceStatus.dwCurrentState = ServiceState.SERVICE_RUNNING;
SetServiceStatus(this.ServiceHandle, ref serviceStatus);

Pls explain what this will do ?

While installing service I'm getting some exceptions saying "assembly not found from the path or incorrect format "