Not a full answer, but here's a collection of related bits of info in no particular order:
* Don't worry about sounding like an idiot. Just be polite and respectful; bartenders prefer polite and clueless over rude know-it-all any day. If it's a busy night, make your mind up before you get to the front of the line so you don't keep the bartender (and other customers) waiting. If you get a last minute bout of indecisiveness, just go for a simple standby like a rum-and-coke.
* Tipping: if it's a simple drink that's just some alcohol and a mixer (eg. rum and coke), $1 per drink is usually fine, just as you'd do with beer. If it's more complex, and involves shaking, straining, muddling or whatever else, consider tipping more. ($2 for a $9 cocktail is reasonable, given that the bartender could have served up two $4 beers with a $1 tip each otherwise in that time.)
* Practice this phrase and use if often: "...and a glass of water, please." Pretty much any bar will happily pour you a glass of water with your drink for free - whereas you'd have to pay $3 or so for a bottle of water if bought separately. Stay reasonably well hydrated to avoid the worst of hangovers.
* Most bars will essentially have the same set of basic spirits to play with - usually some selection of well-known brands of vodka/rum/gin/whiskey/tequila; and then various other liquors in all flavors of the rainbow. Two given bars may not have exactly the same set of name brand whiskeys, for example, but they'll still have at least a couple to choose from.
* The possible exception to this is some bars that focus on a specific type of spirit; eg. some bars may have an extensive selection of whiskeys/scotch or tequilas; asking for a "whiskey" there might be a bit like going to a Starbucks and asking for "coffee". But chances are if you're in one of these bars, you'll know it - they'll list their selection in a menu or on a chalkboard - and have something specific in mind (and will pay a premium for it too!). And these places typically have a full selection of the other spirits too.
* Be sure to use the phrases "oh, what did you get? Can I try a bit?" when hanging out with friends. This is the best way to try new things without committing to a full serving of something you might not like. This is probably how many people discover their favorite drink.
* At a basic approximation, drinks break down into a few common categories; the simplest two are single pours of just one type of spirit (eg. getting a scotch on the rocks - I think this is done usually just for whiskey-family and tequilas); and getting a simple single spirit plus mixer (gin and tonic, rum and coke, whiskey and ginger ale, vodka and orange juice - the last one being often called a screwdriver). You can pretty much order any of these in any bar. The other category is mixed drinks or cocktails, that have more complicated preparation and usually involve one or two base spirits and other ingredients.
* There's a set of well-known cocktails that you can get just about anywhere regardless of whether they are on the menu or not. These include eg. martinis manhattan, margarita, cosmopolitan, lemon drop, appletini and so on. Google for "classic cocktails" or similar to see various lists of these on the web. Named drinks on a menu are often house speciality drinks specific to a particular bar/restaurant. Sometimes, though, these are just variations on well-known cocktails.
* Shots - I'm not going to mention them other than to say that they generally don't have the same name as other mixed drinks.
* Terminology - sooner or later you'll come across "Well drinks" vs "call drinks": Basic idea here is that in most places if you just ask for say "rum and coke", without specifying a brand name for the rum, you'll get a basic cheap generic rum, usually one that's in a bottle in an easy-to-reach (for the bartender) area behind the counter, alongside the tools and ice - called the "well". On the other hand, you can ask for a specific brand - say "bacardi and coke" or "captain morgan and coke" - and you'll get that specific brand; this is called a "call". Generally, a call is more expensive than a well, and may (or may not) be of better quality. While some bars do have cheap wells (with brand names you'd never hear of but only see on the lower shelf at the liquor stores), some others just use decent well-known mid-shelf brands, and it's all the same price; it can vary by bar. Calling is done usually with spirit+mixer drinks - like the examples above - but also for some cocktails, notably martinis/manhattans: eg. you might order a "Tanquery martini" to be sure you got one with that brand of gin rather than whatever they are using in the well.
* Another terminology thing: some drinks you can get "up" or "on the rocks"/"in a rocks glass"; depending on the place and the drink you order, you could get asked which you want. "up" just means in a martini-style glass; "rocks" means a short tumbler (usually with ice).
* Another terminology thing that's good to know: 'Martini' can mean different things to different people. Originally it meant a drink that was mostly gin with a touch of vermouth. Then it came to mean a vodka-based drink to a large group of people. And it can also mean "any mixed drink served in one of those martini glasses with the angled sides". Depending on where you are and who your with, you may need to be specific about what you are looking for. Or if you're getting a drink for someone, and they ask you for a 'martini', be sure to ask them what type.