Reg Portal Development

Hi,

I am pretty new to SAP. Basically I am a Java Developer.

I would like to know where to start off with and what are all the thing which I need to know about Portal Development in SAP so that I can gain some knowledge in SAP Portal Development.

I would appreciate if you could send me some useful links or materials related to this.

Note: I am totally new to SAP and Portal.

Please Advise.