Дурно пахнет: smells funky
There you are in the kitchen, opening a forgotten container of leftovers or cutting open the plastic wrap on some meat you bought and forgot. Pause to retch, then fling open the window and grab your room freshener. It stinks in here.
Пахнуть is the verb for things and creatures that smell. Like the English verb, пахнуть is neutral and can be used to describe scents both heavenly and hellish. But also like English, if used without a qualifier like хорошо (good), it usually means the smell is foul. Тут пахнет (it smells in here) means it smells bad.
And just like in English, smelling bad can be figurative as well as literal. Это обвинение дурно пахнет (That accusation smells funky).
Things that give off a slight smell — usually unpleasant — are described by the verb припахивать. When you shove the questionable meat under your significant other's nose and give the command Понюхай! (Smell it!), the response might be: Да, припахивает. Но есть можно. (Yes, it smells a bit. But we can still eat it.)
If the smell is a bit stronger, the response might be: Мясо с душком (The meat is starting to go off).
If your significant other doesn't share your sensitivity to smells, the response might be: Ничего не слышу, which sounds like the non sequitur "I don't hear anything," but is actually colloquial Russian for "Can't smell a thing."
But if it really stinks, the verb to use is вонять. Фу! Воняет тухлятиной! (Ew! It smells rotten!)
The verb вонять has two related nouns, вонь and вонючка. Вонь is a bad smell, which uses the verb стоять (literally "to stand"). Ужасающая вонь стояла в подъезде (There was a horrible smell in the entryway).
Вонючка is a rather sweet word to describe something or someone stinky, literally or figuratively. You might call a child вонючка when he smells of mud and rotten leaves, or when he does something naughty. Or if you testing perfumes and find one that you don't like, you might exclaim, Какая вонючка! (What a stinky smell!)
Вонючка is also what Russians call a skunk, that bane of American suburbanites' life. In my experience, Russians are almost always overjoyed the first time they catch a whiff of one of those creatures that they've read about but never seen — or smelled.
Это вонючка, что ли?! (Is that really a skunk?), they ask, practically clapping their hands in pleasure. To which I respond: Помыл бы собаку, которую вонючка обрызгала (You ought to try washing a dog that got sprayed by a skunk).
Вонять and the perfective навонять have another meaning that leads us into the territory of Russian words you must know but should not use in polite company. Кто тут навонял? means "who passed wind?"
Of course, in polite company one pretends that one doesn't notice, but if it must be discussed, портить воздух (literally "to foul the air") is probably the least offensive expression.
In families or among close friends, you might hear the verb пукать (to pass gas), especially when referring to little children or dogs, who always seem surprised by – and usually proud of — the sound and smell they produce.
In the locker room you might hear the verb пердеть (to pass gas) or the verb бздеть, which describes the phenomenon American kids call SBD: silent, but deadly.
Вонючка? Это вонь!