Hi,
You need to allow the system to have aggregated-devices:
set chassis aggregated-devices ethernet device-count 1
( if you need more devices change the number to the devices you need)
Next step is to put the interfaces you want to you in the ae bundle: ( you can add to upto 8 interfaces in an ae Bundle)
set interfaces ge-0/1/0 description "ge-0/1/0 <---> ge-1/0/0.otherdevice"
set interfaces ge-0/1/0 ether-options 802.3ad ae0
set interfaces ge-0/2/0 description "ge-0/2/0 <---> ge-2/0/0.otherdevice"
set interfaces ge-0/2/0 ether-options 802.3ad ae0
#Configure the ae0 interface (bundled ae device)
set interfaces ae0 description "ae0.mx <---> aeX.otherdice"
set interfaces ae0 aggregated-ether-options link-speed 1g
set interfaces ae0 aggregated-ether-options lacp active
#allow vlan tagging on the bundled ae interface
set interfaces ae0 vlan-tagging
#config the vlan tag on the sub-interface and IP
set interfaces ae0 unit 50 description "vlan50"
set interfaces ae0 unit 50 vlan-id 50
set interfaces ae0 unit 50 family inet address 10.10.10.2/30
#add the interface to your logical system
set routing-instances <name-of-logical-system> interface ae0.50
Hope this helps you a little