I want to know that where should i need to write & how to install the custom codings. Can some one help me?
Everything you need is here.
https://developer.atlassian.com/display/JIRADEV/JIRA+Developer+Documentation
Recommend starting with the web fragments example if you are writing your first plugin.It's simple and you just need to follow the steps in the documentation below.
https://developer.atlassian.com/display/JIRADEV/Web+Fragments+-+Examples
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