Step 1: Materials needed
the wood we used was cheap, unfinished 1"x8" (nominally 1" thick by 8" wide, but actually 0.75" by 7.25") spruce typically used for decking, under finished siding or sub-flooring; for a longer-lasting - but considerably more expensive - bin, consider using cedar or pressure-treated wood (do *not* use pressure-treated wood that's older than a couple of years, as it may contain arsenic; the stuff you find in stores now does not contain arsenic and is deemed safe for projects like this).
corner posts were 4' long 2"x2"s, pressure-treated (nominally 2" , but actually about 1.5"); they probably don't need to be quite this long, but this will depend on how deep you want your bin to be and how soft your ground is.
for tools, you will need:
measuring tape and pencil;
saw (either hand saw, jig saw or table saw);
hammer and chisel (or flat blade screwdriver);
optional coffee can or similar to slip over corner posts when hammering into ground to prevent damage to top of post.