The tutorial has a section on mosaic assembly with nip2: see §2.2.
Mosaic assembly is normally painless. There are a few factors you should bear in mind when you are deciding how to assemble an image (particularly a large image):
If you join a strip of 10 images together with Tasks / Mosaic / One Point / Left to Right, on average you can expect a total error of about 5 pixels. If you join two strips like this together top-bottom, you can therefore expect a mismatch of about 2.5 pixels at each end of the join.
You can minimise the effect of these errors if you assemble your images differently. Suppose you have a 10 by 10 mosaic to build. Instead of making and joining 10 strips of 10 images each, make four 5 by 5 sub-mosaics (one for each quadrant) and then join these four quadrants together. The errors will now be more evenly spread over the image and therefore will be less visible.