The camera app is linked to the gallery so when u take a picture and want to see a preview, you just tap the tiny image of the picture you took, (in the top right corner of my optimus S but maybe different for you). That image quickly pops up, and by scrolling or using slideshow you can see all the pics on the camera.
The last time you used the camera you probably closed it when you were still at the preview screen. Whenever you do that, the very next time you open the camera app, it will open to the preview screen again, not the camera.
From the preview screen just hit the back button one time and it will take you right back to the camera app.