Blocks is a database for searching domains of the query protein sequence.  To use Blocks, first go to the BCM Search Launcher, then from the menu, choose General Protein Search, and then choose Blocks Search / Blocks in the middle of the page.  You can paste a protein sequence in the space provided, and simply click perform search. 

Then after a while, the search result will be displayed.  At the beginning of the page, it will tell you the details of Blocks, then go to the Hits section, the predicted domains of the protein will be shown, you can click on the hyperlink for details of a particular domain.