Can someone please tell me what to do? Must i open port 1812 and 1813 so that packets can be accepted?

These ports are open by default.

Do you have proper RADIUS client (/radius) configuration on the RouterOS ?
Make sure you have properly configured RADIUS server to communicate with RouterOS.

Can someone please tell me what to do? Must i open port 1812 and 1813 so that packets can be accepted?

User Manager only responds to Radius requests, which are received from a trusted host - called "Router" in the User Manager. To add trusted host, you have to add router.

And check, if the secret used by both the radius client and User Manager (secret is specified per router) are equal.