Here are instructions on how to configure a Nexus 5K with a FEX line card.  This is for connecting one FEX to one Nexus5K using two connections that we will put into a port-channel.

On the Nexus 5K:

NEXUS5K#configure terminal
NEXUS5K(config)#interface ethernet1/1
NEXUS5K(config-if)#description UPLINK TO FEX101
NEXUS5K(config-if)#switchport mode fex-fabric
NEXUS5K(config-if)#fex associate 101
NEXUS5K(config-if)#exit

NEXUS5K(config)#interface ethernet1/2
NEXUS5K(config-if)#description UPLINK TO FEX101
NEXUS5K(config-if)#switchport mode fex-fabric
NEXUS5K(config-if)#fex associate 101
NEXUS5K(config-if)#exit

At this point the Nexus 5K should see the FEX and start the image download.  Once this is completed you can configure the interfaces into a port-channel.

NEXUS5K(config)#interface port-channel 101
NEXUS5K(config-if)#switchport mode fex-fabric
NEXUS5K(config-if)#fex associate 101
NEXUS5K(config-if)#exit

NEXUS5K(config)#interface ethernet 1/1
NEXUS5K(config-if)#channel-group 101
NEXUS5K(config-if)#exit

NEXUS5K(config)#interface ethernet1/2
NEXUS5K(config-if)#channel-group 101
NEXUS5K(config-if)#end
NEXUS5K#copy run start

At this point you should have your FEX connected to your Nexus 5K and be able to configure the ports.

*for some reason my screenshots will not load today.  I will get them uploaded as soon as the issue 
  