How do you get the Benoni opening achievement?
I'm not sure what is needed for the achievement, but for the position to get a Benoni structure, White needs to play 3. d5 and Black must not reply 3. ... b5, which is the Benko gambit. The main line (called Modern Benoni) is 3. ... e6. White then develops either of the knights (4. Nc3 is the main line) and then there is an exchange of pawns 4. ... exd5 5. cxd5 d6.
Black has other options for the third move, 3. ... e5 leads to Czech Benoni (pawns on c5-d6-e5, a Stonewall-type structure), while 3. ... g6 and 3. ... d6 are more waiting and lead to either of these depending on what Black does with the e-pawn.