All Ancestry databases can be searched individually from their own search page. I'm assuming you are starting from the page for U.S. Passport Applications, 1795-1925.
Database pages typically include a section called Source Information and a section About the Database that will give us more information.
About U.S. Passport Applications, 1795-1925 gives a brief overview of the history of passports in the USA, and gives general advice about what might be found in these records.
The Source Information says:
Source Information Ancestry.com. U.S. Passport Applications, 1795-1925
[database on-line]. Lehi, UT, USA: Ancestry.com Operations, Inc.,
2007. Original data: Selected Passports. National Archives, Washington, D.C.
This doesn't say very much, does it? So you need to read very carefully and not miss the next line, which says:
A full list of sources can be found here.
This extra page of information for the database shows which collections Ancestry has brought together under their 'big umbrella'. Most entries have either US National Archives catalog ID numbers (NAI), or a number referring to their microfilm publications.
You can get more information about the Microfilm publications by looking at NARA's portal on their website: Passport Applications Microfilm. For the entries with NAIs, you can click the link to get to NARA's catalog, or search the entry yourself in the National Archives catalog.
General advice on the records and how to search them is on NARA's page Passport Applications, which says:
Photographs have been required with applications since December 21, 1914.
Reference Information Paper 110, Using Civilian Records for Genealogical Research in the National Archives Washington, DC, Area has a chapter on Passport Applications if you want a guide you can download. The RIP has examples of some passport applications, but the content for an application will vary due to the time period. You'll need to narrow down the date range for when your research subject might have traveled to know whether the application is likely to hold information which is useful to you.
NARA's Passport Applications Microfilm page and the catalog also have links to PDFs describing the contents of each Microcopy publication.
You can also view a presentation on doing research in the Passport Applications on NARA's YouTube channel: Passport Applications, 1795-1925. See also: Using Ancestry.com to Access NARA Records.
If you want to take a look at the record before you decide to subscribe, consider using Ancestry Library Edition at a local library, Family History Center, or a National Archives branch location.