There are two items that you need: the Structure Selector and the Structure Builder. You can get them in one of the following ways: Creative:
0.11 an earlier: they should be in the creative menu
0.12: you can type /ism select and /ism build to get the items. Typing this command will overwrite the current selected slot of your hot bar with either the Structure Selector or Builder Survival:
You can craft the Structure Selector with 8 iron and 1 diamond and the Structure Builder with 7 iron and 2 diamonds. Or you can use the commands (see above). Note that this will overwrite your currently selected hotbar slot.
Click a block with the Structure Selector, and a GUI pops up, with a list of all the structures.
Select the one you want. After that, click on a block where you want to place that structure with the Structure Builder. It will popup with a warning dialog. If you click Yes, the structure will be placed.
Some structures will be placed in the direction you’re facing, some will just be placed one direction. The warning dialog will let you know what’s the case with that build.