I am not a wordpress expert at all but have just gone through the process of installing 5 or 6 plugins and using widgets to create a site for the youth soccer team I coach. The site turned out pretty well but still needs some tweaking.
Plugins often have installation directions but most involve transferring the plugin files to the wp-content/plugins folder of your website. Then, go to the administration of your wp blog and under your "plugins" tab look for the new plugin and click "activate".
Widgets allow easy placement and functionality control of items in your sidebar area of the blog. I believe the most recent release of wordpress, 2.3+ has widget functionality built in. Previous releases require the installation of the widget plugin first. Themes have to be described as "widgetized" or otherwise indicate widget compatible.
To use widgets, look under the presentation tab, then "widgets" and you will see a representation of the current order of your sidebar items and below will be options that can be in your sidebar. It is simply a drag & drop process to change the order of the current items in the sidebar or to move new items into the sidebar. There are many widgets that can be included in your sidebar.
Widgets -
http://widgets.wordpress.com/
Widget Information -
http://automattic.com/code/widgets/