I'm trying to combine line features (trail sections) into a single features. How can this be done in ArcMap?
While editing, select the lines you want to combine and click Editor > Merge.
In the dialog choose the feature you want to keep attributes from.
If you have a lot of features and want to automatically combine them (everything into one, or based on an attribute) you can use the Dissolve tool in ArcToolbox
This tool will create a new feature class. In the "Dissolve Fields" box you can pick which fields to dissolve on (so all features that have attributes that match in that field will be merged together). You can also summarise values in other fields using the Statistics Fields options.