I think of this in terms of Buying Temperature. When someone clicks on an ad, assuming they clicked on it on purpose and not by mistake, it means they responded to a compliance test, so they have enough 'buying temperature' to do so. When buying temperature is high, in sales terms, it has to quickly be consolidated through qualification. So the landing page the user sees after clicking on the ad has to be extremely relevant, super specific, and must validate the concern they have, and also qualify the demographics as much as possible.
Follow up with a multi-step landing page, because if you can convince the user to click "Next" a few times, you condition them into doing that, makes it easier to get them to click the buy button. At every stage you want to ramp up the buying temperature with the copy, then when the buying temperature is highest, you show the next "Next" button, and in the next page, qualify and reward them for making that move.
This is for higher ticket products though, if whatever you're selling is really low ticket or tripwire, you need fewer steps, but I'd still keep it really specific.
If you want the user to browse around the site, redirect them to a blog archive or some other similar content page AFTER they buy. During the buying process you want them to be lazer focused on the next step, without any distraction. My own form pages have no header, no navigational menu, no footer, just the content they need to see and the buttons to move them further down the funnel.