Are you looking for a 3D modelling program that feels very natural to use? If so we have found Sculptris to be great tool. It is very easy to pick up and get started with as the initial learning curve is very small compared to many others. The idea behind how Sculptris works is that it is designed to feel like you are working with clay. You are given tools that allow you to manipulate and sculpt the clay as well as add and remove it.
This free program is a great way jump into artistic 3D modelling that has almost no constraints on your creativity. If you are looking for a way to create precise or mechanical parts this may not be the program for you, but if you want to create organic shapes this is a great choice.
Sculpteo has created a great tutorial that covers the whole creation process with Sculptris. The video does have multi language subtitles but the page is entirely in english. It serves as both an entry level tutorial as well as an advanced tutorial as it does cover how to do a large number of things. If it is your first time touching the program you will likely have to back the video up several times to catch the finer details, but everything except the most basic controls are covered.
One added bonus to using Sculptris is that it generally outputs files that are watertight and able to be sliced properly.