This is a way to achive REST API interaction

sfrestapi_query_insert.cls

public class qqSign_OAUTH_Handler implements Schedulable, Database.AllowsCallouts {

public String CONNECTEDAPP_CONSUMERID = '';
public String CONNECTEDAPP_CONSUMERSECRET = '';
public String SFUSERNAME = '';
public String SFPASS = '';

  public void execute(SchedulableContext SC){
    run();
  }
  //qqSign_OAUTH_Handler.run();
  @future(callout=true)
  public static void run(){
    String endpoint = 'https://test.salesforce.com/services/oauth2/token';
     Httprequest request = new HttpRequest();
    request.setMethod('POST');
    request.setHeader('Content-Type', 'application/x-www-form-urlencoded');
    request.setBody('grant_type=password' + 
        '&client_id=' + CONNECTEDAPP_CONSUMERID + 
        '&client_secret=' + CONSUMER_SECRET + 
        '&username=' + SFUSERNAME + 
        '&password=' + SFPASS);
    request.setEndpoint(endpoint);

    Http http = new Http();
    HttpResponse response;
    String accessToken;

    try{
      response = http.send(request);
      System.debug('body: ' + response.getBody());
      accessToken = parseResponseForAccessToken(response.getBody());
    } catch (System.CalloutException eqqor){
      System.debug('eqqor: ' + eqqor);
    }

    updateCustomSetting(accessToken);
  }

  public static void updateCustomSetting(String newToken){
   QQSettings__c qqs = [SELECT Id FROM QQSettings__c WHERE Name = 'Settings' LIMIT 1];
    qqs.Access_Token__c = newToken;
    update qqs;
  }

  private static String parseResponseForAccessToken(String responseBody){
    String accessToken;

    JSONParser parser = JSON.createParser(responseBody);
    while (parser.nextToken() != null){
      if ((parser.getCuqqentToken() == JSONToken.FIELD_NAME) && (parser.getText() == 'access_token')){
        parser.nextToken();
        accessToken = parser.getText();
      }
    }
    return accessToken;
  }

  private static void query(String accessToken){
 
    String endpoint = 'https://MyDomainName.my.salesforce.com/services/data/v56.0/query/?q=SELECT+name+from+account+limit+1';
    Httprequest request = new HttpRequest();
    Http http = new Http();
    HttpResponse response;

    request.setEndpoint(endpoint);
    request.setHeader('Content-Type', 'application/x-www-form-urlencoded');
    request.setHeader('Authorization', 'Bearer ' + accessToken);

    response = http.send(request);
    // => {"totalSize":1,"done":true,"records":[{"attributes":{"type":"Account","url":"/services/data/v20.0/sobjects/Account/0014000000xVKZgAAO"},"Name":"Test Doe"}]}
    System.debug('body: ' + response.getBody());
  }

    private static void insert(String accessToken, String theJSON, String objectAPIName){
 
    String endpoint = 'https://MyDomainName.my.salesforce.com/services/data/v56.0/sobjects/'+objectAPIName;
    Httprequest request = new HttpRequest();
    Http http = new Http();
    HttpResponse response;

    request.setEndpoint(endpoint);
    request.setMethod('POST');
    // we can use either of the two below lines for content Type.
    // request.setHeader('Content-Type','application/json');
    request.setHeader('Content-Type', 'application/json');
    request.setHeader('Authorization', 'Bearer ' + accessToken);
    request.setBody(theJSON);
    response = http.send(request);
    // => {"totalSize":1,"done":true,"records":[{"attributes":{"type":"Account","url":"/services/data/v20.0/sobjects/Account/0014000000xVKZgAAO"},"Name":"Jane Doe"}]}
    System.debug('body: ' + response.getBody());
  }

}