There are plenty of sitemap generators are available online, just you need to put your website url in sitemap creating section. your sitemap will automatically generated. update your sitemap in your root domain as well as google webmaster tools.
It's very necessary to have a sitemap submits into Google webmaster tool. It helps google crawl and index your web pages fast.
Tool depends on your system that you are using
for example, if you are using WP, you can search plugins like seobyyoast or google xml sitemap plugins from wordpress.
You can create the sitemap on your own its really easy and you can also the create by using the several different software available in the internet market. The most popular is the sitemap generator. If you are using the WordPress than there is a sitemap plugin that you have to install.
You can create sitemap manually by reading this stuff. it helps you to create the sitemap manually. hxxp://blog.doteasy.com/2009/06/23/manually-creating-an-xml-sitemap/.
Your site is in WordPress than there is a plugin Google XML Sitemaps is the best. I personally used this and if you want to create sitemap using the sitemap generator tools than this site is the best resource for almost everyone. hxxps://www.xml-sitemaps.com/.
I'd more perfer to create the sitemap manually if and only if your site is not in WordPress.
@Mary Johnson Sitemap is a vital part of any SEO. XML Sitemap act as a visiting card for Google and other search engines which helps them to understand the existence of various webpages on a website, their priorities and how frequently these pages get updated.
There are many online sitemap creator tools. try search google xml sitemap and you will get list of pages that allows you to create xml sitemap.
But if you are using Wordpress then just installing sitemap xml plugin, you can create your sitemap with some clicks.