Available with Network Analyst license.
What follows is a high-level overview of the collection of user interface components that allows you to access and execute ArcGIS Network Analyst extension functionality.
New Network Dataset wizard
It is not possible to just add a streets feature class to ArcMap and start finding shortest routes or perform other network analyses. Simple features, like the line features that represent streets, are not aware of one another. They don't inherently know what they are connected to—and connectivity is indispensable for network analysis. Network datasets, however, store the connectivity of features. Therefore, instead of using street features directly, you need to create a network dataset in ArcCatalog from the streets, then the ArcGIS Network Analyst extension can reference the network dataset for everything it does.
Creating a network dataset is accomplished with the New Network Dataset wizard, which is accessed from the Catalog window in ArcMap. The wizard guides you through a series of questions so it can create a network dataset that fits your needs.
Network Dataset Properties dialog box
Whether you receive a network dataset from someone else or create your own, you might need to access or change its properties. You can do this with the Network Dataset Properties dialog box, which you can access from the Catalog window in ArcMap.
Network datasets have their own attributes that are separate from their source features' attributes. The following examples demonstrate the kind of information network attributes may provide: the costs of traversing network elements (for example, distance), flow restrictions of elements (one-way streets), and hierarchy level (highway, arterial, local road) an element is part of. The Attributes tab of the Network Dataset Properties dialog box is frequently accessed to add or remove network attributes or change how evaluators calculate the values of attributes.
Network Analyst toolbar
The Network Analyst toolbar in ArcMap provides some general-purpose information and functionality. For example, it lets you know which network dataset, if any, is active; it allows you to inspect the attributes of network elements on the map with the Network Identify tool 
; and it allows you to choose the network analysis you want to perform and creates the corresponding network analysis layer for you. Other useful buttons on the toolbar include the Directions button 
, which opens turn-by-turn instructions for routes; the Network Analyst Window button 
, which shows or hides the Network Analyst window; and the Solve button 
, which generates the results for your network analysis.
Network analysis layer
A network analysis layer represents a network problem and, after the problem is solved, represents the solution too. When created, a network analysis layer is simply a generic framework for setting up a network problem, such as a route, service area, or location-allocation problem. You make the generic problem specific by defining properties and populating the analysis layer with data. When the problem is well defined, you can start the solve operation. The analysis layer stores the results.
Network analysis layers are composite layers made up of subordinate layers and are easily identified in the ArcMap table of contents by the lines connecting them to their sublayers.
Network Analyst window
The Network Analyst window in ArcMap is designed to help you quickly and easily manage the inputs and outputs of network analysis layers.
Network analysis layer properties
The Analysis Layer Properties button on the Network Analyst window opens the Layer Properties dialog box, which contains properties specific to the active analysis layer. You can further define the network problem you want to solve with some of these properties. For instance, you can set a property in a route analysis layer that will tell the ArcGIS Network Analyst extension to either determine the least-cost path that visits several stops in a sequence you specify or determine the stop sequence and path that minimizes the overall cost of the route. The Analysis Settings tab contains many of the properties used to define a network problem.
Geoprocessing tools
The ArcGIS Network Analyst extension includes various geoprocessing tools to perform network analysis and work with network datasets and turn features. The tools can be used one at a time or chained together in a model or a script.