questions about jailbreaking, unlocking, and ziphone

okay im totally new to this and ive been looking around these threads and i have a rough idea about how to go about all this unlocking the iphone stuff but im not 100% sure and i want to clarify. so basically i came upon this 3g 8gb iphone that had a cracked screen which i replaced. i want to unlock it but im reading about all this stuff about jailbreaking and what not.

so as to my knowledge it seems to me that you must jailbreak the iphone first then unlock it? what exactly does this mean? im not asking only for instructions on how to do it (though a guide would be helpful) but im curious as to what is exactly being done when you jailbreak the phone, and then unlock it. i want to understand what is actually going on while i do it rather than me blindly following a tutorial.

ive also seen something about ziphone which apparently does everything in one step. anyone have any input on this? i have a pc by the way, which i read ziphone is not currently working on windows but i dont know about that for sure.

thanks!! any information is greatly appreciated.