The advanced options are used for more fine grained operations on the execution.
Fixed Lots (i.e. positions): Risk mode is by default set to 1 lot or 1 unit of a contract or security. This means that every time there is a signal the algorithm executes n unit of that security. For a Forex contract it would for instance execute one Standard Lot by default. For an equity it will buy one share of that instrument.
Auto: Auto is based on a percentage of equity calculation. Depending the account balance, stop loss and risk % it automatically calculates the position size. The account balance for backtest could be changed from the user profile settings. The calculation that appears shows the current position size. As transactions are performed the account balance is affected and positions sizes are automatically adjusted.
Trading day start/end: Controls the days and hours where trading takes place. There is a choice of closing a position either at the end of the day or at the end of the week.
Walkforward Percentage: This is the percentage of the data that the optimized parameters will be tested on. This is used to avoid overfitting based on the optimization period and parameters. A good value is between 20% and 30% to ensure that there is enough data to optimize the data and a handful of data for testing the optimized strategy parameters.
Spread: Spread is used to apply a spread on the bid and ask prices. It provides means of factoring in uncertainty for simulating volatility or slippages. It will apply the value on each side of the trade.
Broker Commission: This is a monetary amount that will get added every time there is a transaction (i.e. buy or sell).