This is a strat called “Box Smoke B”. To start this off, you want to rush into tuns.
Go to the pillar directly to your left, go into the corner and look at the entrance to site. (GEN. DIRECTION)
In that direction you will see on the frame a little edge, to the right of it. You want to aim level to it, and to the left. Left click throw it, and wait for it to pop.
Once you have waited for it to pop you want to have 2 go to the left of the smoke clearing back of plat, also known as back box. Afterwards you want someone to get onto the box, (preferably with a smg) and clear car.
Once this is cleared, you should have 2 done. If the team is any smart, they should have 2 coming from mid, and 1 going through tuns. Make one of your teammates smoke off door for the crossover, and later into the round molly off scout.
You should pick off the one going through tuns if you have one molly there to stunt him. After the delay you should pick him off easily. If the enemy is on eco, they can/will rush, if they have guns then they will save. You want to exit through tuns to lower, and stay until the bomb blows.
Throughout this round, you should have picked off at least 3 people if 2 go onto site and wait for a push. I will add video on how to do this push this afternoon.