Have a look at the man page for ln to find out something about hard and soft links:
Or if you want it with some clear examples and lots of extra information you can find it here at this link
About the types of files you 'have' in Linux, have a look at the man page for magic:
You can also look at this page
for a (limited) list of file types, or you can have a look at the magicfile on your system. That's the file used by the command file when you want to get information about a file. Do a search to find where exactly your file is, but it should be somewhere in /usr/share.