The following requires that the 3-D Analyst extension be enabled in ArcGIS.  For detailed instructions on the use of 3D Analyst, see ArcGIS Desktop Help under Extensions - 3D Analyst.

Before creating a TIN from contour lines, make sure you have clipped the contour lines to the smallest possible area. The TIN creation and analysis puts a huge strain on our computer processing capabilities and the smaller the area the better this will work.

Follow these steps to build a TIN (note that a TIN can be built just from contour lines, or from mutliple sources):

1. Before you begin, explore the data you will be using - this can include contour lines and spot height points (it could also include things like streams to be used as break lines and a boundary polygon to set the limits of the TIN). You will need to know what attribute field contains the elevation information. Make sure that all data sets have defined coordinate systems and that they are in the same coordinate system. Also, the elevation units should be the same units as the horizontal coordinage system units (e.g., both feet or both meters) - See Working with XYZ units.
2. Add the elevation data to your data frame - in this example we assume you are using contour lines and spot height elevations
3. Enable the 3D Analyst extension and open its menu (View - Toolbars)
4. Open the data table for contour lines and spot heights and sort the Elevation field (or other field containing the elevation information).
5. Inspect the data to find "outliers" (i.e., data that is too low [typically 0], too high, or blank.) If necessary, exclude improper data by using the Query tool to select all the incorrect records, start editing the layer, and delete these records. Save edited layer and stop editing.
6. From the 3D Analyst menu, choose 3D Analyst - Create/Modify TIN - Create TIN from Features. The TIN function will show whatever layers are available  for making the TIN.
7. In the Create New TIN dialog, click on the contour line theme and set the Height Source to be the attrbribute field containing the elevation information (for Austin contourlines, this is elevation), set Triangulate As from to Mass Points, and leave the TagValue field set to  <none>.  If you are also using a boundary polygon, then also click on this theme and specify this will be used as a soft clip polgyon with no height information. If you are using the spot heights, click on this theme, choose Triangulate as Mass Points, and specify height source as the elevation value field. If you are using a stream layer, these typically have no elevation value so set that  to none, and triangulate as a hard break line (streams always mark a break in slope).
8. Specify an appropriate folder location and filename.
9. Click OK.

The TIN creation process will take a while.

To create a slope grid from the TIN,  from the 3D Analyst menu, choose 3D Analyst - Surface Analysis - Slope (warning: this assumes that your elevation and horizontal units are in the same unit, e.g., both feet. If they are not, use the Z factor to convert height units to the horizontal units. See Working with XYZ units.

To create a aspect grid from the TIN, make the TIN-theme active, choose 3D Analyst - Surface Analysis - Aspect .

You can display the TIN as 3D in ArcScene or ArcGlobe. You can also drape other layers over the TIN in those programs.

There are many other features you can use, but these are the basics.  Good luck!

Example of a 3-D image created in ArcView by Cesar Escalante - it shows the area around Shoal Creek and Lamar just north of the river.