You first need to upload a file to your Dropbox account.
They give you 2 gb of space on the free accounts.
For files that you are sharing, it’s easiest to create a folder for the files via the icons near the top right. Once the file/files are loaded, you can click on the SHARE button to allow a friend to get the file. Enter their email address and they will get an email telling them that they can get the file that was shared.
Your friend does need to first setup an account.
From the Download link and down arrow, they can either download the file to their computer or copy it to their Dropbox account.