LOL man. i'm gonna try my best to help you out.
tbl, tbsp, tblsp = tablespoon
tsp = teaspoon
so you add 2 tsp (teaspoon) for 1 gallon of water. Basically what you do is you get a 1 gallon container and put 2 tsp (teaspoon) of Grow Big in it. After thats done, get 200ml of that nuted water and poor on plant. You don't have to use 200 ml, i just do it because i feel that its enough for my 1 gallon pot. Another way of feeding is by feeding it untill you see water drop out the drain holes. I'm not sure if this might burn up your plant.
Most people use a reservor, like lets say a 6 gallon container. So that means they need to put 12 tsp (teaspoon) of Grow Big. They use the container because they feel that the temperature of the water might help the plant, plus a air pump that helps circulate the added nutes.
I don't think your suppose to do it by the growing pot size. If you think about it, are you really going to poor 3 gallon of water into a 3 gallon growing pot?
200 ml = 0.2 L (20% of a Liter)
200 ml = 0.05 gal (5% of a gallon)
I hope this help, best of luck bro.