5 pool is when you build one drone (with the starting 4, you will then have 5), then wait for 200 minerals and build a spawning pool, then another drone, then one overlord, then when the spawning pool is ready you will have 150 minerals to build 6 zlings and rush the enemy really soon (don't forget to use the first overlord to scout, tought.
9 pool is the same, but you only build the spawing pool at the 9th probe
Eco means economy. The ammount of minerals and gas you have at the moment and the probabilites that it won't get to zero when you most need it. You need to work well on eco, it's quite important. And you also need to work on destroying the enemy eco