Inside Looking Out hit the nail on the head. Avoid those shops, unless you know exactly what you're looking for. Never take unindentifiable pills or substances, and yes, sex pills are unidentifiable, cause you don't know what the fuck is in those things. That's fucking stupid. Also, drug dealers love the uninformed, just so they could rip them off. Be smarter than your dealer.
Instead of being a sheer asshole, which would be a lot easier on my part, I'll give you some links.
http://www.grasscity.com < Go to their forums, search for anything you are curious about, educate yourself, and if you STILL have questions, ASK THEM THERE.
http://www.stoneddates.com < That's primarily a pothead "eHarmony" thing, but there's a few informational sections that should help you out.
http://www.cannabishq.com < More information.
It seems like you're REALLY REALLY curious about weed, so there you go.
Also, some good measurements to know:
7 grams = Quarter
14 grams = Half ounce
28 grams = Ounce
If you're just starting out, and you're smoking with a few friends, an eighth or a quarter, depending on the amount of friends, should be good enough.
If you already "know" all this stuff, then I am sorry, I guess you're fucked.