Not meant to be exhaustive, there's just literally nothing on here about it so I thought I should give a brief summary since I linked it. Feel free to expand/correct as you may deem necessary.
The "Sunshine Policy" is basically an effort by the South Korean Government to increase the level of co-operation between North and South Korea, and also relax the (constant) tensions between Seoul and Pyeongyang. In the past, Seoul has been pretty harsh to the North, especially in terms of economic sanctions. This has mainly been in response to (frankly) the dicketry of the North Korean leadership, which routinely issues threats, provocations, and even commits terrorist acts against SK.
Two main motivations behind the Sunshine Policy. It is broadly, generally popular with the South Korean people, who feel sympathy with their northern neighbours while (of course) despising the NK government. The second main reason behind it is the fact that sanctions and constant back and forth retaliation isn't really effective here. Especially since both sides appear to privately acknowledge that neither can achieve military victory at a reasonable price. So for a while the South would bend over backwards, even to the point of ignoring blatant violations of the armistice agreement (this still happens often, even though it was never official policy), for the North. Lots of economic aid goes more or less straight to the NK government, and there are even joint NK-SK communities and a shared factory town inside the DMZ. Isn't that nice?
The present administration in SK (since 2008) has adopted a more mixed policy of carrot-and-stick, honey AND vinegar, with the North. Aid is tighter and increasingly coming from private hands, for example, and when the NK Navy strays too far into South Korean waters, it gets shot up, which is encouraging.
Rather than giving away stuff for free, as was the case previously (past 10 years), the current SK leadership is adopting firm positions on the expansion of "shared" projects such as the Kaesong industrial plant, because apparently we don't like the North having nuclear weapons. Is the policy successful? Hmm, well Seoul hasn't been completely obliterated at the time of writing and I don't hear any sirens, so this reporter says maybe.
Limited economic and political engagement has seemed so far
to be effective in bringing the NK leaders to the table, although they
tend to run around firing shots into the air once you've given them
some rice.
Most people who don't live on the Korean Peninsula are pretty unaware of the fact that this warzone is very much live, the two Armed Forces frequently exchange fire and the tensions are pretty high. Especially now that the SK and USA naval embargo on NK shipping of nuclear technology and material is (apparently) going to be enforced. THAT could lead to some serious escalation, but is probably unavoidable.