Resources are a form of currency within OGame. The main resources are Metal, Crystal, and Deuterium. Metal and Crystal are acquired through Basic Income and debris fields, All three can be acquired from any of the three mines, trade, or through raiding. In addition to the main three resources, there is a special resource known as Dark Matter. This resource can be gained through expeditions, or can be purchased via the 'Officers recruitment' tab.
The production from mines is listed as an hourly rate, and your stock is updated as each unit is produced. For instance, a level 9 Metal Mine has a production rate of 636 units per hour. So, if you refreshed your screen every minute you would see an increase of about 10.6 metal each minute.
The OGame software treats all resources as equivalent in terms of point value, but in fact, some resources are more difficult to produce than others. A level x metal mine produces more metal than a level x crystal mine produces crystal, which in turn produces more units of crystal than a level x deuterium synthesizer produces of deuterium.
The conversion factors are summarized in the table below. This is a starting rate for trade, though it changes quickly due to supply and demand and, in the case of deuterium, the temperature of the planet the deuterium is being mined on.