It's highly complex, but actually quite simple in its complexity. Once you understand what is being done with the multiplicity of files, you can look at an element on a page and realize what the item base function is and immediately follow the folders down to the actual code block that produces that element.
Abandon what you know about relational database function, in EAV, all the columns have been converted to rows and put into tables according to data type which then get keyed by a multiplicity of type, entity, attribute and other ID's. Getting data out of a table requires the select statement to have numerous self-joins in order to extract rows by the particular typeID, attributeID, etc to extract the value. The EAV concept is actually extremely old and simple to understand, the implementation to actually extract data using SQL is horrendously complicated, use Magento's collection mechanisms to work with data, you'll be a lot happier.
Only fools attempt to run Magento on shared hosting unless they never intend on being successful and attracting a large quantity of customers. The first time a triumvirate of search engines hits a site with more than 500 products, the system falls flat on its face. Give it a dedicated quad core server with memory and tune mysql and your APC cache to start on the path to running a serious Magento website.