Yes, this is a BIG question ...
What is Fitted Mesh?
Fitted Mesh is a technique in which an avatar's collision bones are used to add further deformation detail to an avatar or clothing. The benefit of this technique is that it allows Mesh clothing and avatars to be adjusted using an avatar's Body Shape sliders in the Appearance Editor. This results in clothing that can adjust and fit to your avatar's own personal body shape and style.How do I know what I purchased?
First of all you have to have the most compatible viewers to wear it. If you have not upgraded your viewers you can not see it hint #1. Hint #2 is if you cant adjust your sliders while wearing it then its not Liquid/Fitted Mesh (see video below).
Why do some designers sell one size and others sell with 5 sizes?
Easy answer and not.. Some designers feel that since it is one size fits most it is easy to sell one size. Although Fitted Mesh is supposed grow with your avatar there are still some limitations. The Sellers with 5 sizes are catering to a broader consumer. My suggestion is and critical advice is to DEMO first. Put the outfit demos on, adjust your sliders see if the Mesh moves. Always stay informed and always stay informed!WHAT VIEWERS CURRENTLY SUPPORT FITTED MESH?
As of March 20, 2014 the following viewers support Fitted MeshOfficial Second Life Viewer – Update Version: 3.7.3.287491
Firestorm Viewer – Update Version: 4.6.1.40478
Singularity Viewer – Update Version 1.8.5(5617)
Black Dragon Viewer (Nirans Viewer) Update Version: 2.3.9.3
If you are using any of these viewers but are not able to see fitted mesh correctly please update your viewer to the newest version. There may be other viewers that I am not aware of that also support fitted mesh! Please update whatever viewer you use to see if it does in fact support fitted mesh. If after you update you still do not see fitted mesh correctly please download one of the viewers listed above.
Appliers?
Appliers are not needed with Fitted/Liquid Mesh. That defeats the purpose of using this new technology for mesh clothing. Appliers are used for Mesh bodies, breasts, booties, etc. Since you are unable to fit mesh clothing over these enhancements, designers create "Appliers". Fitted/Liquid Mesh adjusts with body sliders so you can wear beautifully designed mesh products without adjusting your SL Avatar Shape. Why not wear 3D clothes on Second Life?Article Resources and Links
Rigged Mesh vs. Fitted/Liquid Mesh Watch video below
Links
http://community.secondlife.com/t5/Featured-News/Making-Mesh-Garments-Fit-Better/ba-p/2336599
http://community.secondlife.com/t5/Featured-News/Fitted-Mesh-Is-Here/ba-p/2461687
http://wiki.secondlife.com/wiki/Mesh/Rigging_Fitted_Mesh
http://community.secondlife.com/t5/English-Knowledge-Base/Controlling-your-avatar-s-appearance/ta-p/700709