When you run into issues with your OpenERP installation or you have questions about specific features, one of the best resources available is the official OpenERP help site. The site is simple in such a way that you can search for specific questions, and if you find that your specific question has not been addressed, you can then ask your own question. This is the URL: http://help.openerp.com.
OpenERP 7.0 is typically downloaded in a format that already comes with many modules available for installation. However, there are many more modules in the online repository. If you are thinking about making any customization in OpenERP, check out this link to make sure someone else has not already done the work for you: https://apps.openerp.com/.
While it is kind of buried and has a funny URL, this is a good resource for changes in OpenERP 7: http://v6.openerp.com/node/1272.