I go to installers, then module, then browse the picture (banner) that I want to upload, and it gives me an error.
It is asking me for a "package". I don't know what a package is. How can I upload a single picture?

Installing a module needs a "package", a zip file that is.
Trying to upload a picture is not installing a module.
What exactly are you trying to do?

You need to go to http://extensions.joomla.org/ to find the module you want to install, download the zip or tar.gz file and upload it in the backend. Then when you go to Modules you'll see it listed. If the module is already installed, then open it up in Modules and configure it to your liking. Please post which module you are trying to work with.

If you want to upload a banner go to media manager the images the banners. You must upload your banner there.
Then go to components banner and publish the banner from there.
If you want a module which is really a different thing altogether you must download the module you want and install it as you are trying to.
Please download the official user manual from www.joomla.org. You will save you self lots of trouble