When i go into "Mods" and click one, i get redirected to steam workshop, is it possible to get custom mods on Don't Starve GOG version?

Also, can anyone explain the DLC to me?

The DLC is pretty basic. It adds some items to the game, provides an expanded set of seasons and weather types, and gives you more monsters to worry about. It also changes the mechanics a bit to accommodate the new seasons and weather types, if I'm not mistaken. Of course this is all configurable in the world creation settings.

You can download the mods at Klei's Forum. Here's an example: Summons