In the case of collusion, the students involved would be deliberately trying to deceive the tutor who is marking their work by allowing another student to copy their work and then presenting it as their own, or vice-versa.
A more difficult example of collusion would be students working in a project group. In this situation it must be clear to the tutor which student has completed which sections of the group’s project. Students must write their sections separately, otherwise they could be suspected of collusion.
You must also ensure you understand the assessment guidelines before you start work. If these are unclear, then ask your tutor to clarify.
Remember, in professional life you will regularly be collaborating with colleagues but will still need to clearly identify your own work. Be completely transparent about what you as an individual have done by keeping a clear audit trail.