There are 3 step-by-step tutorials and several segmentation recipes on the training page of the latest Slicer version.
You can also find lots of questions and answers about segmentation on this forum (see segmentation tag or use the search function).
You may get help at any of the Slicer weekly hangouts or if you attend a Slicer project week.
If any of your questions are not answered, feel free to post it as a new topic in this forum.