According to the Company Act 2013 a public limited is a company that has limited liability and which offers its shares to the general public. Company's stock can be acquired by anyone whether privately through (IPO) initial public offering or through trades on the stock market. It is strictly regulated and is required to publish its true financial health to its shareholders.
As the above answer has covered up most of the basics about Public Ltd Company i would like to add on about the-
Requirements/ Registration of Public limited Companies
1. 7 minimum shareholders and 3 directors
2. minimum share capital is Rs 5lakh
3. Digital signature certificate of one of the directors.
4. application for selection of company name.
5. Submitting application to ROC along with documents like AOA,MOA, dully filled form DIR-12, Form INC-7, and Form INC-22
6. payment of prescribed registration fees
7. Application for the certificate of business commencement after approval from the ROC.