Written assignments like essays and reports are often submitted on the VLE.
Submission points are found either in a specific module VLE site or in a special assessments site for all modules on your course.
Formative assignments (useful for developmental feedback on your work) are likely to be set up with Blackboard Learn Ultra (as opposed to Blackboard Original).
Summative assignments (that count towards your grade) are likely to be set up with TurnItIn.
Our student guide to submitting assignments explains more.