Documentation to user-defined/custom fields in JIRA

We are planning to create custom fields in JIRA and to link our instance to other software. Do you have any documentation/information that could be of use for us?

The following links could be helpful to you:
https://confluence.atlassian.com/display/AdminJIRAServer071/Adding+a+custom+field
https://confluence.atlassian.com/adminjiraserver071/configuring-a-custom-field-802592532.html
https://confluence.atlassian.com/jira064/adding-a-custom-field-720412132.html

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