Welcome to the List-Category-Posts wiki!
You can select one category by id or name, several categories, exclude categories, and more. Check this page for instructions on selecting which posts to show.
There's a ton of parameters you can use. Check this page to learn which ones and what they do.
Read how to paginate your posts lists.
You can customize almost every way the plugin displays your posts' information. Check which elements you can customize just by setting some parameters and writing a few CSS classes. CSS knowledge is required.
More advanced display customization. Some PHP, HTML and CSS knowledge is needed for you to be able to build your own custom template.
The widget is pretty simple.