Where can I purchase Bitcoin?

Could you possibly elaborate on the various avenues available for procuring Bitcoin? I'm particularly interested in understanding the reliability and security of these platforms. Additionally, are there any specific factors I should take into account when choosing a platform to make my purchase? For instance, do transaction fees vary between platforms? And, how do I ensure that the platform I choose is legitimate and trustworthy? Also, are there any regional restrictions that might limit my options? I would greatly appreciate any insights or advice you could provide on this matter.