A sprint — also known as an iteration — is a short period in which the development team implements and delivers a discrete and potentially shippable application increment, e.g. a working milestone version. If you haven't run sprints before, we recommend using a fixed two-week duration for each sprint. It's long enough to get something accomplished, but not so long that the team isn't getting regular feedback.
Note: Sprints do not apply to Kanban projects.
In Jira Software, you view sprints on a board and assign issues to sprints. You can search for issues in upcoming sprints using JQL (Sprint field). You can view the Sprint field on each individual issue as well, to see the sprint that an issue is part of.