Jira lets you add custom fields and lets you provide descriptions for those custom fields (to guide users). However the New Issue View in Jira does not use or display these custom field descriptions in any way.

One possible implementation is:

When a user hovers over a field in the new issue view. display a ? which can then be clicked or hovered-over to display the field description text. When the field loses focus then the ? icon disappears to reduce clutter on the screen.

Discussed in community post https://community.atlassian.com/t5/Jira-Software-questions/When-where-do-I-see-the-description-of-a-field-in-the-new-issue/qaq-p/1270966?utm_source=atlcomm&utm_medium=email&utm_campaign=immediate_general_reply&utm_content=topic