Voltage regulators in SPICE software
If you mean how to write the netlist, then it will be something like:

XU1 N001 0 N001 N002 +10V LT1761-SD

The above is an adjustable regulator with 5 pins (IN, OUT, GND, ADJ and SHDN)

It's a subcircuit, so it's declared with an X. Also, since complex subcircuits are usually written in a separate file, you need to make sure the subcircuit file is included in the netlist with a declaration like:

.lib LT1761.lib

Alternatively you can add the subcircuit code directly into the netlist.
I would recommend LTSpice, it's an excellent, easy/quick to use and powerful free SPICE.