Line Following Robot with Arduino Nano


I am working on a project where I have to design a Line following Robot with Arduino Nano. I am using Infrared sensor below the robot and they are detecting the black line.

So, I have made it able to follow a simple black line but now I want it to make turns so can anyone please help me out here ???

Can I make an exact 90 degree turn with it or I have to make a curved turn ???

Also I need some help with Detection of turn, how it will know that now I have to make a turn?

I hope I am cleared, if you need more info then I am happy to provide.