Many geoprocessing tools have parameters that allow you to use multiple values for processing, for example:
The Merge tool, which combines a number of datasets into a single output dataset, has the Input Datasets parameter in which you select or browse to multiple datasets.
The Multiple Ring Buffer tool has the Distances parameter in which you specify multiple distances to buffer around the input features.
The Summary Statistics tool has a Case field parameter in which you specify one or many attribute fields from the input table that will be used for row aggregation.
The Delete Field tool has a Drop Field parameter in which you select one or many attribute fields from the input table that will be deleted.
When working with a parameter that accepts multiple values, press the Enter key to add another value to the list. Click the empty area inside the box to select a row in the list of multiple values. Select one or many rows and press the Delete key to remove those values.
Some parameters that accept multiple values have an Add Many button that allows you to select multiple items from one list.
Click the button to select multiple items and add them to the parameter list.