HI

I add name for one table to 2nd table via script ,I want to add only in empty portal row  ( example if firt portal row is empty name come to first portal , if not empty goes to 2nd row and so on .... 

how if add a script step that i do that , 

That's not very clear. If you want the script to create a new child record, where will the values to populate the new record's fields come from?

Anyway, you have two options:

1. You can tell your script to Go to Portal Row [Last] and populate the fields there; or
2. You can create the new record directly in the child table, without using the portal.

In general, if you do not require user interaction in creating the record, the 2nd option is preferable as it works directly at the data level and does not rely on any layout objects (such as portals).