There are several cases for making an HTTP request from a host application to another Atlassian application, for example:

Typically these are done through calls to the REST API of the other application, or to a script endpoint. However you can also use remote events, or remote control to do the same thing.

Which approach you use depends on the specifics of the task in hand.

For how-to questions please ask on Atlassian Answers where there is a very active community. Adaptavist staff are also likely to respond there.

Ask a question about ScriptRunner for JIRA, for for Bitbucket Server, or for Confluence.