Here's an explanation of the Effects from FAQ2.01. Towards the end it explains the use of sends and how to use the sends with tracks:
-How do I use the Effects in the Command Station, I don't understand the Sends?
There are two Effects processors available in the Command Stations at any time, regardless of whether you're only playing a single Preset, or a Pattern with 16 Tracks. You can use the Effects in one of two ways, each selected from the Global menu. The first is where the Preset on the active MIDI channel controls the Effects, and therefore all the Effects settings are used as stored with that Preset. This way works best if you're only playing a single Preset at a time.
The second method for using the Effects is in Master Effects mode. In this case, all Presets share the same two Effects, and the Effects and their settings are saved as a part of each Pattern. However being able to only turn the Effects on or off for each part is not very flexible, so E-Mu uses Effect Sends to increase your options. Just like there are only two Effects for the entire Command Station, there are only four Sends for the entire unit as well. The send amounts for each effect are freely assignable in the Global menu. For instance, say your first effect is a reverb, and your second is a delay. You can specify how much reverb you want to be applied to Send 1, as well as how much Delay you want to be applied to Send 1. Say you set your reverb amount to 5% on Send 1, and your delay amount to 27% on Send 1. In this configuration, any Track you route to Send 1, will have about 5% reverb on it, and then it has 27% of the delay effect added to it. If you only wanted reverb for instance, you would just set the delay amount for that Send to 0%, and now all Tracks routed to Send 1 will only have reverb applied. You can assign more than one Track to a Send, and you have 4 Sends to use for each whole Pattern, giving you lots of ways to use only those two Effects processors.