Modules are blocks of code that get loaded/installed into your drupal site
that give you expanded/additional functionality.
Every Drupal installation, whatever version, will have a set of core modules included.
What modules are installed?
log into your site with admin password
click Modules in top menu bar.
a page will open with a list of all your installed modules,
with columns showing their enabled/disabled status,
if the enabled box is checked but grey, that means do not disable it because other modules depend on it.
their version#, plus a description of what they do.
At the top of this page there may be a warning block telling you that some of your modules
need to be updated - their version# does not match your current drupal core version.
click "available updates" for more info
Install new modules:
on Module list page, click "install new module"
If you know the name/url of the module you want, enter it in the top field.
however this must be a link to a .tar.gz archive file.
If you have previously downloaded a module (.tar.gz) that you now want to install,
click browse and navigate to its location on your PC and install