If you search google your bound to find tons and tons of Second Life tutorials, though some maybe great your new at this and just don't understand some of the things they are trying to show you. You need the basics before you try those out.

The first thing you will need is a editing program and I don't mean MSPaint people! Im talking Photoshop, Gimp and others such as that. If you don't already have Photoshop and don't have the money to go buy it (yes it's expensive) then you can get gimp for free at http://gimp.org/ Sadly though most tutorials I find tend to be photoshop. The next thing you wil need is base templates. What are these? These are the second life clothing templates you will need to use as guides to make clothing. There are a couple different ones and you will have to try them out for yourself to figure out which ones you like best.

  1. Linden Lab Clothing Templates: http://secondlife.com/community/templates.php 
  2. Robin Wood's Clothing Templates: http://www.robinwood.com/Catalog/Technical/SL-Tuts/SLPages/AVUVTemplates.html

Now for the tutorials:

Photoshop Beginner Tutorials
Creating Your First Shirt - http://nicolaescher.com/tutorials/creating-your-first-shirt
Basic T-Shirt Tutorial (Video) - http://www.youtube.com/watch?v=nbzCfHy2JXc&feature=fvw

Gimp Beginner Tutorials
Making Clothing (Video) - http://www.youtube.com/watch?v=mT5ULiZ5pqA&feature=related
A lot about making SL clothing is getting use to the program you use and many of there features, taking time out just to play around with features tends to help your clothing creations a ton. Not everyone does things the same, find out what works for you!