Making a file available on the internet for anyone to view and download is called hosting.
Once a file is hosted, it can be viewed, downloaded, and displayed on webpages and email signatures. Typically, you would purchase web hosting from the same companies that you purchase domain names from, such as GoDaddy or 1&1, for an additional monthly or yearly fee. Now with cloud storage services such as Dropbox and Google Drive, your files are already hosted online, so it's just a matter of directing people to those files.
To use a hosted file in a website or email signature, you need the direct link.
A direct link is the URL that points directly to your file hosted online. By "directly", I mean no additional "junk" around the file. No webpage code, just the file, thanks. For a file to have a direct link, it needs to be hosted and publicly available online. Once you have the direct link to a hosted file, you can paste it anywhere online (including in the right place your email signature) for people to view or download the file.
The instructions below will tell you how to get the direct link to your files in Google Drive so use can use them online where you need them. You can do this with Dropbox as well, but the instructions will be different.