Quick tour of communicating with features
Features are an effective way to communicate or highlight important things on the map. A feature is a point, line, area, or text displayed on the map that may have associated information such as an image, video or text that's displayed in a pop-up window.
Features in can be stored in a map, or reference features that come from a service running on a GIS server. You work with both types of features in much the same way.
All features in a map are contained within layers. Click the Layers tab in the left side panel to show the Layers panel and see the layers that are in the map. You can change the visibility of an entire layer of features by checking or unchecking the check box next to the layer.
Each feature stored in the map is listed in the Layer Details view of the Layers panel; click the arrow to the right of the layer name to open the Layer Details view for a layer. You can double-click a feature to zoom to it, and change the feature visibility by checking or unchecking the check box beside it. You can also define the scales at which the features will be drawn on the map by configuring a scale range. Features that come from a service are not listed in Layer Details, but you can apply a filter to restrict the features that are visible in the map.
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Creating features with ArcGIS Explorer Online is easy. Click the Add Features tab in the left side panel to display the feature templates available for the layers in the map. Choose the type of feature you want to create from the templates, then click or drag your mouse on the map to create your new feature.
For features stored in the map, you can change the way a feature is drawn by clicking the Change Symbol button 
on the toolbar to display the Symbol drop-down panel. Choose a symbol from one of the symbol gallery, or click the find icon 
at the top of the panel to search for a symbol by keyword. You can change a symbols size (for points and text), width (lines and polygon outlines), and font (text). You can also change the opacity, and for some symbols you can change other properties too. Once you have you feature looking the way you want, you can create a new feature template to create more features just like it.
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For features that come from a service, you can change the way the features are drawn again in Layer Details, by clicking the Configure button under Display. You can draw the layer based on the values of attributes, and also classify the layer by numerical values.
To display the pop-up window for a feature, click the feature on the map. You can configure pop-up windows for features that don't already display them, again using Layer Details.
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To add content to the pop-up window of a feature, click the feature to open its pop-up window, click Edit at the bottom of the pop-up window, then click Edit Pop-up. When you've finished specifying the content, click OK to see the updated content in the pop-up window. A feature may not have a pop-up window by default; if required, you can add and configure pop-up windows for all the features in a layer.
Learn more about:
Changing how features are displayed
Working with feature templates