You need to have a Blackberry Data Plan and you may need to update your phone using http://us.blackberry.com/update/

All Google apps should be downloaded using the Blackberry Browser which must be set to Internet Browser  (possible change is to use your suppliers Browser) and Browser Identification to Blackberry (open Browser – menu - Options - Browser Configuration to see this) and using the address http://m.google.com should take you to a Google home page that will lead to the downloads or if you are sure of the official designation of the app you want you can append this to the address bar as /##### so this could be /mail or /sync.

When you download and install any Google App you need to  Enable Security settings because if you don’t this would cause problems. Can be corrected by going into Options (spanner/wrench)  - Security Options - Application Permissions (New versions of BB’s Operating System 5 and above– use Applications) - find the Google app in question and highlight - menu - Edit Permissions - make them all Allow.