sitemap.xml, sitemap1.xml, sitemap.html, sitemap1.html ??????

I have a question about the following:

"Google doesn't support sitemap files with more than 50,000 pages. That's why script supports "Sitemap Index" creation for the big sites. So, it will create one sitemap index file and multiple sitemap files with 50 thousand pages each.
For instance, your website has about 140,000 pages. The XML sitemap generator will create these files:
"sitemap.xml" - sitemap index file that includes links to other files (filename depends on what you entered in the "Save sitemap to" field)
"sitemap1.xml" - sitemap file (URLs from 1 to 50,000)
"sitemap2.xml" - sitemap file (URLs from 50,001 to 100,000)
"sitemap3.xml" - sitemap file (URLs from 100,001 to 140,000)
Please make sure all of these files are writable if your website is large.
Enable "Create HTML Sitemap" option to let generator create a sitemap for your visitors. You should also define the "HTML Sitemap filename" where the sitemap will be stored. It is possible to split html sitemap onto multiple files by defining the "Number of links per page in HTML sitemap" option.
The filenames are like the following:
"sitemap.html" - in case when all links fit in one file
OR
"sitemap1.html" - site map file, page 1
"sitemap2.html" - site map file, page 2
etc

Same as point above: please make sure all of these files are writable. "

Does this mean that I will have to create and upload separate files named "sitemap1.xml", "sitemap2.xml", "sitemap1.html", "sitemap2.html" etc. as well as having already uploaded "sitemap.xml"?
OR
Does the generator create these files?
ALSO
There is no "sitemap.html" file included to upload. Is it created by the generator using "sitemap_tpl.html" or do I have to create and upload my own "sitemap.html" file?

The above is not really clear.

If anyone knows the answer to this please post here.