Extractor modules extract one item every 100 ticks (5 seconds) from the inventory they are connected to, like a powered wooden pipe, and insert them into the network.
Extractor modules have sneaky functionality (they can be configured to behave as if they are attached to a side other than the one they are actually attached to).
It can also extract from an Applied Energistics network through an ME interface, everything in the network is extracted (except for items the extractor is configured to ignore).
The Mark2 version extracts 1 item per 20 ticks (1 second and equivalent to a fully warmed up redstone engine).
The Mark 3 version extracts 64 items per tick (prior to Minecraft 1.6.2 this needs the BuildCraft items per pipe limit in the Buildcraft configuration file to be increased to at least 1000 to work properly and with full speed).
Advanced versions of each mark of extractor are available. The advanced extractor modules extract at the same speed as the standard version of corresponding mark but also have a GUI to set items to include and exclude from being extracted.