Grid system like opening trades in SELL or BUY direction and between each trade is amount of pips, the main goal of Grid system is if the direction of the trend continue you still open trades against the trend to recover when the market opposite its direction
there is also some Grid system use hedging to open trades in both sides
For Example: 1st trade is 0.01 sell EURUSD on 1.24100 but the trend goes up and reach 1.24400 you open another trade on 1.24400 by 0.02 but the market still in Bullish and reach 1.24700 and you grid strategy open another 3rd sell position by 0.04 then the market start to bearish and go down till 1.24400 and you close all your trades.
The calculation will be 3rd position 0.04 x 300 pips = 12$ the 2nd position 0.02 x 0 pips = 0$ the 1st position 0.01 x 300 = 3$ total profit will be 9$
Most grid systems use fixed pip distance ignoring price action, which makes them risky even without martingale.
Price action sensitive grid systems are much better specially when they fade micro trends in favor of the main trend.