In order to save a camera angle (meaning both the camera position and the direction you are pointing the camera), click the "Save Camera Angle" button on the HUD.
The camera angle will be saved under a name consisting of the coordinates of the camera position by default. You can change the name of the angle by typing
/25 new camera angle name
in local chat immediately after you clicked the "Save camera angle" button.
To restore a saved camera angle, you can either click one of the "Previous/Next Camera Angle" HUD buttons to cycle through all the camera angles you have saved so far.
Alternatively, if you know the name of an angle, you could pick it by name in the menu under "Choose Angle".
Note that the camera angles are saved per-region, which means that the angles are only available in the same region ("sim") you saved them. When you enter another sim you will get a different set of camera angles.
Important note: Due to a restriction of the Second Life client, the script can modify the camera position only if it is in default mode, i.e. if the camera position and angle hasn't been altered using the Second Life viewer camera controls. To switch back to the standard camera position, press the "Escape" key to release the camera control.
When you're done with the camera angle, release the scripted camera and return to the normal camera mode by clicking the "Stop" button on the HUD.