Hi Monalisa!

We think the best way to do this is to add a lookup field on the account object to this custom object - so then you can have multiple accounts associated with one record from this custom object.  Technically it is possible to accomplish this the way you say, using Javascript to take the Account Ids and appending them to a long text area, but it would involve a lot of coding - so we think adding a lookup to the account object to this custom object will be the best long term solution.

By “multiple data”, do you mean multiple fields from the one record that the lookup is set to?
By “store in a longtextarea” do you mean an editable and saveable text field? or a read only field that displays on the child record?

no, multiple data means suppose i want to select 2 account object ids at a time and store in a long text area separated by semicolon.long text area will be a readonly field.

This will be a custom javascript solution.  Here is a sketch. Build a model that has the account objects as multiple rows.  Build a javascript snippet that calls that account model and goes through each row ($.each) and appends the account id to a temporary field,  with a semicolon after the ID.  Then after spinning throuhg the models update the data in your long text area with the value of your temporary field.  

Review our javascript API for more details here. http://help.skuidify.com/m/11720/c/51305