Hi jongkp,
The Dynax 300si is basically a point and shoot camera in a SLR body. There's no aperture, shutter priority or manual mode. It has a few programmed modes like in landscape, sports, night scene, etc, which means you have not much control over the settings that you wish to take the shot in.
However, since it has a SLR body, you can use the whole range of lenses and flashes.
Wouldn't recommend you getting this unless you are looking for point and shoot ease of use in a SLR camera. You might want to consider getting Dynax 5 series to start with. At least it offers decent functionality for photography.
Cheers!