The very simplest way would be to create a new droplet from the LAMP one-click image (this is overkill for the purpose but will do the job). Once your droplet is created you can use a client like FileZilla to make an SFTP connection to your droplet and upload the file(s) you wish to share to /var/www/html

Note: The LAMP image will install a database server and PHP which are not needed for this. Another option would be to simply install the web server alone. To do this, start by creating your droplet from the Ubuntu 16.04 image. Once it's finished being created, ssh into the droplet.

Once you're connected run the following commands:

apt-get update
apt-get -y install apache2

Once this is complete you can use Filezilla to upload your files to /var/www/html