Please go through SECP website, Jama Punji website, and study different details there, and if you make up your mind and if Stock Exchange suits you, then go for investment in it, but then, I would suggest avoid going there directly / solely.
Prefer to invest via AMCs (Asset Management Companies), and in this, NBP Fund Management Limited, Al Meezan Investment Management Limited and MCB-Arif Habib Savings and Investments Limited are the best, with highest PACRA ratings, AM1, as of today (Still, Meezan is better. Still, NBP is the best in these 03).
Go through the relevant websites (PACRA, NBP Funds, Al Meezan Investment official websites, etc.) and if NBP Funds suits you, then go for NBP Stock Funds, or NBP Islamic Stock Funds (if wanna go Shariah Complaint).
I hope, it helps and guides a bit. Thank you.