Mark G, look for the "Play Store" icon. That's for the Google Play (app) store. Lots of free stuff on there to download and install.
I use File Manager (Explorer) by Cheetah Mobile, but there are plenty of other choices available.
The Google play store site is accessible on the
web via your PC (play.google.com). You can go there
and browse available apps. You can search the site
for free file manager, or whatever.
When you find an app that looks interesting,
read the features. Scroll down, past the reviews,
to the "additional information". On the right
is a title called "Permissions", with nothing
under it but a link reading "view details".
Click that. It will tell you what information
your free app will lift from your phone and
send to the company providing the app, which will
then sell it on to whatever corporations or
agencies have an interest in such things.
As a user with a healthy paranoia, I imagine you
will find this information highly illuminating.
If you want a "free" app that does not stripmine
your phone of all of your personal information,
you will probably find that the only things available
are GNU public license open source items of limited
functionality. All the really nifty and well constructed
free apps are bait from big data mining companies.