Automatically Populate fields - HELP!

Automatically Populate fields - HELP!

There have been many discussions on this but I still can't seem to get it to work for me. I am trying to create a lookup field and have other fields automatically populate. Based on the instructions in the Help Center, I should be using the "on user input". It's just not working, here is the layout...
 
Both forms are in the same application. Current form is called Add Note, form to fetch records from is called Add Client. Lookup field is called Select_Client_ID related field in fetch form is called Client_ID. The fields I need to populate are Last_Name, First_Name, Phone_1 and Phone_2. In the fetch form those fields are called LastName, FirstName, Phone1 and Phone2. Someone please show me the exact script if you can. I've written several ways and can't get it to work. Thanks so much.
 
Please help!