For adding new items please watch the adding new items video linked below, this will take you though all the steps for setting up your items basic information.
Once you have all the basic info set for your item now in the Inventory Actions add a new option by selecting the + icon. Then set the Inventory Actions to Place. Then set the Action Name to anything you like as this is the text thats displayed in the options menu when you right click the item.
Next set the QuickUseAction to Place, this means if the item is set in the quick bar and you activate the item using the key bound to that quick slot the item will be used to place the build part.
Next set go to the Build Part Details, the set the Data Table to MasterBuildPartList. Last set the Row Name to the build part that you want the item to place. Once this is done your finished and can use the item to place build parts by either right clicking it in the inventory and selecting the PLACE option or dragging the item to a quick slot and pressing the key that quick slot is bound to.