By itself, MODX doesn't come with much in the way of extra functionality. This is provided by add-on packages. Let's install the add-ons we'll be using; these are the packages most commonly needed for basic site functionality. Go to System -> Package Management, and click on the Download Extras button. This will take you to the official MODX add-on repository. You can browse for add-ons in various categories, or you can use the search field to get to add-ons that you know you want to download.
We want to download several packages:
Once these are downloaded, click Back to Package Management. Your newly downloaded packages will show, with green Install buttons for each. Go ahead and install them.