Are these all frigin' pajamas or what??

Am I the only one who doesn't understand baby clothes? They ALL look like pajamas to me; do I dress them in this stuff to go out too?? Seriously I'm not trying to be funny but I was trying to go through the clothes we have and see what else we need (more shoes!). What does sleep n' play mean? They generally have the little feet on them so I figured "okay these will be pajamas." But then I started coming across sleep n' plays without feet and they look more clothes like so I didn't know what to do with those. Why do they need sleep n' plays if they could just wear onsies and sleep in those. And onsies...is this all they will be wearing? He'll be born in July so it should be nice and toasty out so do I just put an onsie on him and that's it? Is that acceptable; is that what they are for? Or does he need pants too? How many pairs of pants should I have for his first 3 months? And socks will he need to wear socks? That seems kind of funny to me wearing socks with a onsie, like me walking around in my bra and underwear and a pair of socks. All the little baby clothes that actually resemble adult size clothing are not in newborn sizes. I understand a little pair of jeans or cargo pants are not pajamas but it's this other stuff that has me lost. And when do they wear the tight little knit, hats? I know the hospital gives them a couple but its July, should he be wearing one all the time? In the house? I'm gonna end up clothing my son to death I can see it. He'll either have too much on or not enough. As you can tell I've had very little experience with people under 12 months old.

Off topic I wanted to mention how great my husband is as preparing me for motherhood. This morning while in my deep slumber, which is very rare these days that I even remotely get into a deep sleep, I am scared shitless at this this God-awful shrieking, baby whaling at the top of its lungs. It turns out my husband sneaked into the bedroom and hid the baby monitor (which was at max volume by the way) and proceeded to cry like a baby while in the nursery. I guess he was testing my reflexes but if my baby has lungs like my husband's, I'm going to be in the insane asylum within 3 days.