I am new with salesforce, I have an Apex class and I would like to create a test for this class but I have no idea, can someone help me please

public class NouveauProduitExtensions {

    public NouveauProduitExtensions(ApexPages.StandardController controller) {
    }
    
    public PageReference cancel() {
        return Page.Nouveau_produit;
    }
    public JointMatProd__c Jointure {get; set;} 

    public Produit__c prod { get; set; }

    public NouveauProduitExtensions() {
        prod = new Produit__c();
        Jointure = new JointMatProd__c();
    }
    
    public PageReference showAddMatierePage() {
        return Page.Produit_Add_Matiere;
    }
    
    public PageReference Save() {
        insert prod;
        insert Jointure;
        PageReference acctPage = new ApexPages.StandardController(prod).view();

        acctPage.setRedirect(true);

        return acctPage;
    }

     public List<cMatiere> matiereList {get; set;}
     public List<JointMatProd__c> JointList {get; set;}
     public List<MatierePremiere__c> selectedMatieres{get;set;}
     public Integer value {get;set;} 

     public List<cMatiere> getMatieres() 

     {
      if(matiereList == null) {
       matiereList = new List<cMatiere>();
       for(MatierePremiere__c c : [select Id, Name, Unite__c from MatierePremiere__c])
    
       {

       matiereList.add(new cMatiere(c));
       }
      }
      return matiereList;
     }  
    
public PageReference processSelected()

 {
  
   
    selectedMatieres = new List<MatierePremiere__c>();
    JointList = new List<JointMatProd__c>();
    
    for (cMatiere cMat : getMatieres()) {
        if(cMat.selected == true) {
            selectedMatieres.add(cMat.mat);
        }
    }
   value = selectedMatieres.size();
   System.debug('printing listcontc'+selectedMatieres.size());
    
    for (MatierePremiere__c mat : selectedMatieres)
     {
        JointList.add(new jointMatProd__c(Produit__c = prod.id, MatierePremiere__c = mat.id, Quantite__c=0));
    }

   return page.Nouveau_produit;

 }

public class cMatiere

{
 public MatierePremiere__c mat {get; set;}
 public Boolean selected {get; set;}

 public cMatiere(MatierePremiere__c c) {
            mat = c;
            selected = false;
        }
  }


}