Referred the link for SharePoint rest api integration 

Sharepoint Website Create

1.Visit https://<subdomain>.sharepoint.com/_layouts/15/sharepoint.aspx

2. Click on Create Site

3.Select "Team Site"  

1. Enter Site Name as per project
2. Enter Description
3. Click on Next

4.When click on Next show the option to add additional member

5. 

6.Click On finish to create site.

1. Register Add-In

navigate to https://edeltech.SharePoint.com/sites/<SiteName>/_layouts/15/appregnew.aspx and enter Add-In application data to generate client id and clinet secret as below:

Client Id: XXXXX

Client Secret: XXXXX

Title: PostMan

App Domain: localhost

Redirect URI: https://localhost

2. Grant Permissions to Add-In

 Navigate to https://<Subdomain>.SharePoint.com/sites/<SiteName>/_layouts/15/appinv.aspx and enter the client id to lookup the registered Add-In. Add following XML as Permission request XML.

<AppPermissionRequests AllowAppOnlyPolicy="true">

<AppPermissionRequest Scope="http://sharepoint/content/sitecollection/web" Right="FullControl" />

</AppPermissionRequests>

Confirm the addition by clicking Trust It.