I am a beginner programming.
I was able to create a controller Visualforce, I have trouble knowing how to create a test.

Will you advise how can I create a test look like?

---Visualforce---

<apex:page showHeader="true" title="入力画面" standardController="nyuuryoku__c" extensions="otamesi">
              <apex:sectionHeader />
              <apex:form >                                           

                         <apex:pageBlock title="値引き商品情報" >
                         <apex:pageBlockButtons >
                               <apex:commandButton value="2.値引き商品計算" action="{!quicksave}" />
                         </apex:pageBlockButtons>
                         <table class="otamesi1table" border="3" style="float:left" width="700" >
                         <tr>
                              <th bgcolor="#9999ff" height="20"></th>
                              <th bgcolor="#9999ff" height="20">商品名</th>
                              <th bgcolor="#9999ff" height="20">商品金額</th>
                              <th bgcolor="#9999ff" height="20">注文台数</th>
                              <th bgcolor="#9999ff" height="20">小計</th>
                          </tr>
                          <tr>
                              <th height="20">値引き商品1</th>
　　　　　　　　　　  <td height="20"><apex:outputField value="{!nyuuryoku__c.nebiki1_name__c}"/></td>
                              <td height="20"><apex:outputField value="{!nyuuryoku__c.nebiki1_nedan__c}"/></td>
                              <td height="20"><apex:inputField value="{!nyuuryoku__c.nebiki1_daisu__c}"/></td>
                              <td rowspan="5" align="center" height="20"><apex:inputField value="{!nyuuryoku__c.nebiki_syoukei__c}"/></td>
                         </tr>
　　                </table>      
              </apex:pageBlock>
       </apex:form>
       <apex:form >      
               <apex:pageBlock title="納品情報" mode="edit" id="up">
                          <apex:pageBlockButtons >
                                <apex:commandButton value="3.支払い情報へ" action="{!siharaisave}" reRender="up,down"/>
                          </apex:pageBlockButtons>
                        <table class="otamesitable2" border="3" style="float:left" wideth="60%" id="down">

　　                     <tr>
                              <th bgcolor="#9999ff" colspan="2" height="20">書類発送日</th>
                              <th bgcolor="#9999ff" colspan="2" height="20">保証書発送先</th>
                              <th bgcolor="#9999ff" colspan="3" height="20">その他の場合</th>
                          </tr>
                          <tr>
                              <td rowspan="3" colspan="2" height="20"><apex:inputField value="{!nyuuryoku__c.syorui_hassou_date__c}"/></td>
                              <td rowspan="3" colspan="2" height="20"><apex:inputField value="{!nyuuryoku__c.hassousaki__c}"/></td>
                              <th height="20">名称</th>
                              <td colspan="2" height="20"><apex:inputField value="{!nyuuryoku__c.hassousaki_name__c}"/></td>
                          </tr>
                          <tr>
                              <th height="20">住所</th>
                              <td colspan="2" height="20"><apex:inputField value="{!nyuuryoku__c.hassousaki_addr__c}"/></td>
                          </tr>
                          <tr>
                              <th height="20">電話番号</th>
                              <td colspan="2" height="20"><apex:inputField value="{!nyuuryoku__c.hassousaki_tel__c}"/></td>
                          </tr>
                      </table>
                 </apex:pageBlock>
       </apex:form>
       <apex:form >    
                 <apex:pageBlock title="支払い情報">
                          <apex:pageBlockButtons >
                                  <apex:commandButton value="4.確認ページへ" action="{!save}" />
                          </apex:pageBlockButtons>       
                         <table class="otamesitable3" border="3" style="float:left" width="700">
                         <tr>
                             <th bgcolor="#9999ff" height="20">支払い回数</th>
                             <th bgcolor="#9999ff" height="20">支払い方法</th>
                             <th bgcolor="#9999ff" height="20">支払期日</th>
                             <th bgcolor="#9999ff" height="20">支払額</th>
　　                     </tr>
                         <tr>
                             <th height="20">1回</th>
                             <td height="20"><apex:inputField value="{!nyuuryoku__c.X1__c}"/></td>
                             <td height="20"><apex:inputField value="{!nyuuryoku__c.siharaikijitu1__c}"/></td>
                             <td height="20"><apex:inputField value="{!nyuuryoku__c.siharai1__c}"/></td>
                         </tr>                      
                     </table>
             </apex:pageBlock>
       </apex:form>
</apex:page>

---Controller---

public class otamesi{
      nyuuryoku__c nyu;
      private ApexPages.StandardController con;
     
      public otamesi(ApexPages.StandardController stdController){
      this.nyu =(nyuuryoku__c)stdController.getRecord();
      con = stdController;
      }
     
      public  void siharaisave(){
      nyu =(nyuuryoku__c)con.getRecord();
         nyu.Flg1__c = true;
         con.save();
      }
          
      public PageReference save(){
      nyu =(nyuuryoku__c)con.getRecord();
         nyu.Flg2__c = true;
         return con.save();
      }
     
}