Android supports L2TP/IPsec since version 4.2x. If you have an older version, you need to choose another protocol.
Open the system settings.
 
Be sure you are in "Connections" tab and tap "More networks" menu item.
 
Tap "VPN" in order to get to VPN connections settings.
 
On "VPN" screen tap "+" sign at top right side of screen.
 
Fill VPN Connection form with next values.
    Name: Trust.Zone-Japan
    Type: L2TP/IPSec PSK
    Server address: jp.trust.zone
    IPsec pre-shared key: trustzone
         Trust.Zone-Japan
        jp.trust.zone
        trustzone
        Trust.Zone-Japan
        jp.trust.zone
        trustzone
    
Tap "Show advanced settings" and be sure that "Forwarding routes" is set to 0.0.0.0/0. Then tap "Save".
         jp.trust.zone
        jp.trust.zone
    
If all goes well, you should see new VPN connection, so tap it if you want to connect.
         Trust.Zone-Japan
        Trust.Zone-Japan
    
Put your username and password and check "Save account information" on if you want Android to remember your login credentials. Then tap "Connect".
    Your Username: HIDDEN. Log in or Sign up to see.
    Your Password: HIDDEN. Log in or Sign up to see.
         
        
        
    
If connection has been successfully established, you will see "Connected" near your VPN connection name as well as "key" sign in notification area.
         Trust.Zone-Japan
        Trust.Zone-Japan
    
Open Trust.Zone Main page or reload it if it is already open in order to check if your connection with Trust.Zone VPN is established correctly. 
You can also visit our Connection Check Page.
     Your IP: x.x.x.x ·
    
                                     Your IP: x.x.x.x ·  Japan · 
        
            You are in TRUST.ZONE now! Your real location is hidden!
        Japan · 
        
            You are in TRUST.ZONE now! Your real location is hidden!