In this iLogic tutorial the assembly is a simple manifold block with flange fittings that are held on with socket head cap screws. The block is the first part placed into the assembly.
Click
the Place tool from the Inventor Assemble
ribbon tab.
A grounded occurrence of the component is placed in the assembly with the part origin aligned with the assembly origin. A second occurrence of the part is attached to your cursor in the event that you want to place another. In this case you do not.

In addition to the block, this assembly will consist of a set of 3 union caps, and 3 sets of screws to attach the caps.
Add Union_Cap Components
Click the Place tool once more.
Double-click union_cap.ipt.
In the Place Standard iPart dialog box, choose the iPart member Union-01 (Part Number U-050) under the Table tab.
Click in the graphics window to place the union near the manifold block. Add three unions, then Dismiss the Place Standard iPart dialog.