Autodesk Inventor is different than AutoCAD.
In fact, it is more like AutoCAD Mechanical Desktop. It
uses Sketches
to define 2D geometry with dimensions.
Then the 2D geometry is made 3D by one of several commands.
The 2D geometry can still be changed and updated like Mechanical
Desktop. AutoCAD doesn't allow easy changes to the 2D geometry.
This allows much more versatility in edited geometry once created.
The sketches and 3D conversion are easy to change at any time.
Inventor also has Constraints
that mate parts together.
When you have two or more parts you can define how they meet and
change that constraint later through direct editting. Way Cool!
Learn Autodesk Inventor by using it.
Start by sketching a 2D shape and add dimensions (if you want). Then tell Inventor how you want to make it a solid. Put parts together by defining the relationship between the parts. Drawings are as simple as placing the desired views where you want them on the paper size you want. Sections and details are created automatically.