Plugins are fairly easy to install.
In your WP admin, go to Plugins -> Add New and then search for something like "poll".
You'll get a number of results, and then it's up to you to find the one you like. You can click on Details for each plugin to see if it matches your needs, and if it does, you can click on Install Now to add it to your site.
Once you've installed one, you'll probably have to configure it and place it on any page/sidebar you like, but how that works exactly, usually differs between the various plugins.
So to answer your question: yes, installing is easy. Configuring it can be a different thing but that depends on how each plugin is coded.