In which of Plato's works did he present his concept of Platonic Ideas?

He doesn't just present them in one of his works, rather in many. You can find a lot of the idea of Forms in the Phaedo, the Protagoras, the Parmendies, the Republic, and some in the Euthyphro. Yes, there are elements of the Forms in the other works as well. But, these few works listed above will definitely be an est if you are planning on reading to better understand the Forms.