Hi,
Below are the things you need to look into:
1. Look into your organization structure.
2. Prepare an Employee Personal File and maintain MIS where you have to include details such as their offer letter, appointment letter, confirmation, promotion, joining details, address proof, increment letter, etc., in their personal record. In the MIS, include the employee code, name, address, father's name, date of birth, date of joining, date of retirement or retrenchment, and every detail of your employees.
3. Now, you have to build up an idea. It's time to create job descriptions for all your employees.
4. Maintain time records and attendance records of your employees.
5. Assign an employee code to everyone.
6. If you do not have any policies and plans, then work on establishing policies such as leave policy, tour and travel policy, incentive plans, disciplinary policies, etc.
Start with these tasks as there is a lot to do to establish an HR department. I will provide further information later.