Run the ISE "Project Navigator" software.
Select "New project"...
then choose a project name and directory
then click "Next" to select the device (for example for a Pluto-IIx, choose the Spartan-3A XC3S50A in a VQ100 package)
and click "Next" and "Finish".
Click "New Source"...
then select "Verilog Module" and give it a name.
Type the following text (as-is, this is case sensitive):
Click "New Source" again.
Select "Implementation Contraints File", give it a name...
and type the following.
Select the "ledblink" top level, then get to the programming file properties
and make sure to float the unused pins.
Select "Run" and wait a few tens of seconds.
Go to Xilinx's ISE In-Depth Tutorial page.