The verb pair гулять/погулять means “to take a walk.” It is often used with the preposition по followed by the dative case: «Мы погуляли по парку» “We took a walk around the park,” where “around” means “aimlessly here and there through the park” not “in a precise circle around the park.” In the spread-out cities of the American West people don't take walks so much for pleasure nowadays; you practically have to drive to your own kitchen. But in Russia walking around in the evening or the afternoon is still a big part of socializing.

That's actually a common thing to do in St. Petersburg. (The bridges have to open to let boats travel up and down the river.) Or you can stroll around the streets of Moscow after the stores have closed, admiring the buildings and enjoying the eternal twilight of Russian summer evenings. Ugh. Did I really just write “eternal twilight”? What a cliché.

Гулять can also mean “to goof off.” A mother might shout at her son «Боря, чего ты гуляешь во дворе? Ты должен быть в школе!» “Boris, what are doing goofing off in the yard? You're supposed to be at school!”

When a Russian mother can't stand having her child inside anymore, she'll also use this word in the context where an American mother might use the word “play”:

(The phrase «на улице» literally means “on the street,” but the mother isn't saying “Go play in the street” out of some poorly-hidden filicidal wish. Instead «на улице» is one of the standard Russian phrases for “outside.”) Other variations: «Иди погулять» “Go play” and «Сходи на улицу» “Go outside.”

By extension of the “goofing off” meaning, гулять also can mean “to have a good time, party, whoop it up,” which leads us to a joke. It's a joke based on a pun, and puns don't translate well unless the target language has the same duplication of meaning in the punning word as the source language. We'll have to explain it in detail, which means the joke won't be that funny, but what the heck...

So why is this funny? Well, the primary meaning of the “whooping it up” word is “to take a walk,” and the phrase translated “getting started” means “walking” (i.e., walking to the store to buy vodka and get started), so in effect, he is saying “our buddies are already walking around, but we are just walking.” And of course the guy they spotted is already so plastered that he's lying under the fence and can't walk. And he is already so drunk that you can hardly say he is whooping it up. And the guys who are about to get equally plastered are feeling envious of the totally unenviable slob lying there on the ground. Now that's funny... um, right? In a kind of pathetic alcoholic way?