Hi Sanjana,
What you are describing is usually addre3ssed by what's known as PPO (Preplacement offer).
Your organization, just like the regular recruitment process, needs to take the intern into the regular pipeline through this offer, subject to the intern successfully completing his degree/PG course.
Once he accepts your offer, he goes back to his institute to complete the course requirements. During this time, if he is a local person, he may continue to visit your organization in a way that does not violate his institute's requirement.
Also, if his institute has a placement office, it needs to be notified about you making the PPO and the student accepting it. You will then be guided through the institute's placement process.
Once his course is complete and he meets the necessary academic / other criteria, if he has accepted the PPO, then from the commonly agreed date he can start his employment.
As for the probation period, it may be in the organization's interest to retain the provision of probation even if you are offering a PPO to the intern after observing his performance. The candidate may be made permanent earlier, depending on how well he meets the performance milestones.
We hope this helps.
Let us know if you have any follow-up questions.
Best wishes,
Team HRM For Non-HR Managers