Script runner - add request participian based on value in custom field

[Joohny Loo5er]

Hello everyone. I beg for your help. I am not a programmer but I want learn something :)

I need add request participiant to a new ticket based on custom field, which will be filled by customer from picklist during request creation.

I read a few topics here and tried few scripts in post function simple script at Create transition but no one was work.

Can anybody help me with this issue and suggest me solution? 

A will be grateful.

Thank you