Following the free agency period there will be a rule 5 draft. If you choose to totally simulate the draft you will be forced to watch the computer select everything, taking roughly 5 minutes. If you choose to do it yourself, you get to pick who you want. Pick a player. If possible, let the thing sim the rest, as it's a pretty boring activity, and largely wont affect how well you do in the game. If not, just mindlessly pick as you see fit. The achievement should pop following the Rule 5 Draft.