It depens on what yo want to do so i propose 3 ways:
1) (easy and overall) create a surface in GSD (es. Rectangle sketch + fill), then click on it on the tree and select Proprieries, -> graphics -> texture. Make sure your visualization is set To Material ON- This works for most applications
2) If you need images for reference of your model teh best way is Use the Sketch tracer workbench. Learn to use it and it will make it easier to aligh and to crop images with different views. Anyway i can advice that its interface is somehow "obscure"
3) you want just to add a sticker to your model for rendering. This is easy in Photo workbenck. Use the sticker command.. This is easy to use.
Have fun!! And remember CATIA is NOT solidwoks, needs more "thinker" approach and more time ti learn
you are right man, solidworks so simple but catia very hard, sometimes i hate catia,because i should think some commands very hard to understan, i can draww easly solidworks but if i try with catia , i cant do same model, :) maybe i will your help sometimes