Hello @Muhammad_Asif2,
here a link to a thread where you asked a very similar question on gradient descent: Supervised learning - #6 by Muhammad_Asif2 The replies are also relevant here!
For a very good bias explanation, please check this video from Prof. Ng: Lecture 10.4 — Advice For Applying Machine Learning | Diagnosing Bias Vs Variance — [Andrew Ng] - YouTube
It’s important that these basics are well understood since future course material will build on it. Therefore do not hesitate to ask your questions after watching the course videos and doing the necessary course work.
Best
Christian