I'll help you out a bit with a quick overview of all the MIDI you'll probably need to know.
Channels: Any MIDI message is sent on a specific MIDI channel, from 1 to 16. Think of it like having 16 phone lines in your house. All phone calls must come on exactly one channel. If you are standing beside phone number 4 (i.e. channel 4), the person calling you needs to use channel 4 as well, or you won't get their message. Some devices can send or, more commonly, receive on all channels. A message sent on multiple channels really means that two messages are sent out: remember, one message uses exactly one channel.
Message Types: You typically don't need to know how a message is formed or what the parts are, but here are the common types of messages.
Note On/Note Off: Has the note number and velocity. On Korg keyboards, note 0 is C-1 and note 127 is G9.
Program Change: A message telling a MIDI device to switch presets. Programs range from 0-127 (some devices will label them as 1-128). You can use a program change to change the current combi or program on your M50, within the current bank (so if you're in bank C, PC 5 will change to program C-005; there is no way to use a program change to switch banks).
Bank Change: Sometimes combined with a program change, this also switches banks (so you could change from some program in bank C to program B-005).
Aftertouch: The M50 doesn't have this, but it's a measure of the pressure you place on the keys after initially pressing them.
Pitch Bend: This one at least should be pretty obvious
Control Change: MIDI assigns a specific number to various controls, and most keyboards let you assign different numbers to some of the physical controls. For example, a sustain pedal always uses CC #64 and the mod wheel always uses CC #1. It's not good enough though to know that you've moved your mod wheel; the message also has to indicate the position of the wheel, between 0 and 127. Some controls may only send 'on' and 'off' messages, like the sustain pedal, and they'll send values of 127 and 0 typically.
Ok, so what does this mean for your setup?
Well, firstly, you need the M50 to send clock messages to the Electribe on a channel the Electribe is listening to. If you know that you *never* want the M50 to control the Electribe, then you can leave both global channels as they are (they're both probably 1 right now) and follow what X-Trade said about filters. The idea is that the filter makes the Electribe ignore a particular type of message, so you'll have to filter out all the types you don't care about. The clock messages might be categorized under System or Realtime or something similar, so you don't want to filter out that type, of course.
On the other hand, you may decide that at some point you might want the option of controlling the Electribe with the M50's keyboard and other controls. If so, you'll have to do things a bit differently. I'd recommend taking this latter approach, but I won't describe it unless you're interested, to avoid giving you too much detail right now.
Hope this helps!
