How to synchronize issues' fields

Assumption: you already have created the connection and contract.

Field mapping is used to point to remote fields. You can choose which fields you want to synchronize with remote JIRA. 

Local field is a name of a field from issue, which you want to expose, those will be send to the remote JIRA.
Remote Field name is an alias, which will be presented in remote JIRA instance. 

Remote JIRA administrator will be able to consume them and map them to fields in remote (their) issue.  

To edit them just click on "Edit" button, then a dialog will appear.
Here you can add or remove fields you want to send to the remote JIRA instance.
When you finish selecting the fields, just click "Save" button.

"Fields to send" component will refresh and present you the fields you are exposing to remote JIRA instance.