As a starting point, you need to create a sequence node that contains each image slice and its correct position and orientation. This is done automatically if you read your images from an MRI scanner but if you just have a bunch of TIFF files then you need to put together the sequence manually.
First of all, you need to set the origin, spacing, and axis directions for each image slice. The origin is the physical position of one corner of the image, spacing is the size of one pixel, and axis directions are the directions of the x, y, and z (=cross(x,y)) axes of the image, using either the Transforms module, or using SetOrigin, SetSpacing, and SetIJKToRASDirections methods of each volume node. Once all the image slices have the correct geometry, you can put them into a sequence using either Python scripting, or using Sequences module: in Edit tab, choose Sequence → Create new sequence, select each node in the “Add remove data nodes” section, and click the green arrow button until all images are added to the sequence.