* STEP 1 Download and Install SketchUp

SketchUp MAKE/
-This is the FREE version of SketchUp easy to use CAD program

DOWNLOAD SKETCHUP MAKE

* STEP 2 Quickly learn the SketchUp tools

SketchUp Video Tutorials
- Easy short videos to learn SketchUp super quick!

NEW USERS (VIDEO TUTORIALS)
http://www.sketchup.com/intl/en/training/videos/new_to_gsu.html

TIP: Try to learn 1 tool a night and you will have it down in no time.

USERS FAMILIAR with SKETCHUP (VIDEO TUTORIALS)
http://www.sketchup.com/intl/en/training/videos/familiar_with_gsu.html

EXPERTS IN SKETCHUP (VIDEO TUTORIALS)
http://www.sketchup.com/intl/en/training/videos/expert_to_gsu.html

* STEP 3 Install these Extentions to Make SketchUp even better!

Extention Warehouse
http://extensions.sketchup.com/ 

SketchUp has loads of Extentions (Plugins) that are scripts written by users as well as  the SketchUp team. These addons take SketchUp to new levels. If there is somthing that you wish SketchUp could do, look in the Extention Warehouse and more then likely there is a free extention in there that will do just want your after.

Installing extentions is as simple as clicking the install button on the extention page in the warehouse! Cool Stuff

Recomended extentions for SketchUp
-Easy to install FREE plugins that will help your bring your SketchUp models out to the real world. 

-SketchUp STL
This importer lets you import/exprot STL files for SketchUp.
http://extensions.sketchup.com/en/content/sketchup-stl

-SketchUcam (Follow install directions)
The SketchUcam is a set of SketchUp tools that will allow you to create and easy to use CAM solution right in SketchUp!
DOWNLOAD - Sketchucam

More information about SketchUcam can be found here:
http://www.phlatforum.com/viewtopic.php?f=98&t=2

NOW GO EXPLORE!
There are a lot of awesome plugins and tools out there using SketchUp

Check out these cool sites for plugins and cool models:
Phlatforum -  http://www.phlatforum.com/xenforo/
SketchUcation - http://sketchucation.com/forums/
OpenBuilds - http://openbuilds.com/