How can i build something on my own?

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hi everyone im 15 now and really love programming i have done cs50p but not done every problem set yet and sql that i learn some from sqlzoo and pandas ig enough for using and pytorch little but i wanna learn form building project but there 2 thing i wanna ask

1. what i should start from i think of stock prediction i know it gonna hard and too much but i really love start from hard but problem is i dont know how to start from tutorial or something but i wanna build on my own tho so i wanna ask do u guy have any resources or something i can learn from?

2. Logic sometime in leetcode i know how it work sometime i dont so i wanna ask how do you understand how it work i try pesudocode but it not really work so you have any techniques or how u actually thought when u see problem

ty for everyone information i might go sleep now goodnight everyone