Plugin Install?

I am a newbie with a free WordPress hosted site. I am using the Coraline Theme. I would like to install a forum plugin for my site but I haven’t been able to find the Plugin tab under the Dashboard. I have found a couple of materials that I will read later on but will appreciate it if someone can shed some light on how to install plugins within WP and if there is a plugin tab somewhere within the Dashboard.
Thanks in advance for all responses.