How to predict the function of unknown or known protein using Swissprot?

First go http://expasy.org/sprot/ search uniprotkb for protein name (opsin 1) then go at this page it will give this protein in many different organism http://www.uniprot.org/uniprot/?query=opsin%201 so narrow down your search click the fields>> and select any option instead of All like organism [OS] so select in next bar human [9606] and click Add&Search the result of protein family present in humans is appeared as a result click any one of the ID so you can get the information about any protein like its domains and function etc http://www.uniprot.org/uniprot/P08100
I hope you will like it regards "Quratt ul ain Siddique"