Plugins contain code that adds extra abilities to your WordPress website.
For example, the slideshow below was produced using the Meta Slider plugin.
Installing this plugin added an extra section to the WordPress dashboard for putting slides into the slideshow and controlling its appearance, speed etc.
The Website Help site uses several plugins including: Caldera Forms, Lightweight Grid Columns and WordFence Security. Installing these has enabled me to add some extra features to make my site work in the way I wanted.
There are thousands of plugins available from many different developers, but you do have to be a little careful as not all of them are well written and the code could even contain malware.
A good, and relatively safe, place to look for plugins is the WordPress Plugin Directory, which includes reviews by other users. It’s always a good idea to check the reviews, to look at when the plugin was last updated and to see whether there are any outstanding issues on the support page.