To create a sitemap, you can use special services - automatic generators, for example:
1. Mysitemapgenerator.com. In the free version, it allows you to scan up to 500 pages, which is ideal for small portals. Using the paid packages ($ 2.5 and $ 4), you can index from 1 million pages to an unlimited number, setting up a sitemap update on a schedule (useful for portals where new web pages often appear).
2. Gensitemap.ru. Here you can scan up to 1000 pages for free. Paid packages vary depending on the number of pages you need to add to your sitemap.
If your website is developed on any of the common CMS, for example WordPress, then you can use any of the existing plugins - you do not need to use third-party services.
There are a huge number of plugins that generate a sitemap, for example, Google XML Sitemaps, WP Realtime Sitemap.