I'm a bit new to the switches, but I believe it works as such:
1 - Configure your vlan interface
set interfaces vlan unit 1 description Servers
//It is recommended to use the same unit no. as the vlan, for ease of management
set interfaces vlan unit 1 family inet address 10.1.1.1/24
//define the ip
2 - Create your vlan and add the l3 interface
set vlans Servers description "VLAN for my Servers" //create vlan and add description
set vlans Servers vlan-id 1 //802.1q identifier
set vlans Servers l3-interface vlan.1
3 - Associate interface with vlan
set interfaces ge-0/0/0 unit 0 family ethernet-switching vlan members Servers //for an access port
set interfaces ge-1/0/23 unit 0 family ethernet-switching port-mode trunk //for a trunk port
set interfaces ge-1/0/23 unit 0 family ethernet-switching vlan members Servers