But when it comes to the stats:
Slugging is total bases (TBs) divided by ABs, so it's like a batting average with hits weighted by how many bases you get. When you compare it to batting average, you can get an idea of how much power a guy has.
On-base percentage is already factoring in walks, because it's hits, walks, and hbp divided by plate appearances instead of just ABs. So it gives you an idea of what kind of eye a guy has.
One reason OBP comes up so much in the Sabermetrics and the "moneyball" approach is because it's a big factor in Bill James' "Runs Created" stat, which combines OBP and SLG%. Another more commonly reported combo of these is OPS, which is just OBP + SLG. High-ranking OPS players tend to be regarded as some of the best hitters in baseball (Jose Bautista, Miguel Cabrera, Ryan Braun, Matt Kemp, and Prince Fielder were the top 5 in 2011).