How are symmetrical +/- voltage supplies obtained in a final (standalone) design?
When using an AC input to the device a transformer with two seperate windings (or one winding with a tap in the middle) can be used to create a postive and a negative rail.


Source: https://www.quora.com/What-is-a-dual-polarity-power-supply-using-a-transformer-a-full-wave-bridge-and-a-Zener-diode

With only one DC input you typically use a DC/DC converter, like a switching inverter to create the negative rail (see e.g. APPLICATION NOTE 3844 by Maxim Integrated).  

If the needed current is quite small it is a viable and very easy solution to just use a voltage divider with a buffer to create a virtual ground at half the DC voltage. The TLE2426 is actually a ready to use "rail-splitter" to do exactly this.







simulate this circuit &ndash; Schematic created using CircuitLab

When building the above circuit you should choose a Rail-to-Rail OpAmp, otherwise you are limited to quite low output voltages. This circuit only makes sense when the current is not significantly higher than 10 or maybe 20mA.