If someone has sent you an email with a link to view files in Dropbox, accessing the files is as easy as clicking the link.
Depending on how the folder/files were shared with you, authentication via Dropbox.com may be necessary to view the files (shown below).
If you are creating your free login for the first time, you can ignore the portion of the Dropbox sign up that asks you to install their software. It is not needed. The important part is getting a username and password created, so you can login to view the shared folder/files.