Configuring the settings in the Advanced, Expert and Margin tabs of the Tick data settings dialog can be a bit confusing at first.
It's very important to know that by default all the settings used during your backtest are taken from the MT4 account that you are connected with.
These settings are meant to be used only if you are very familiar with what each setting does and would like to override the account settings.
None of the settings has an effect unless the override checkbox next to it is enabled.
If you are not familiar with the effect that these settings can have on your backtest it's best if you leave them alone, the account defaults will suffice for most cases.
If you wish to find out more information about these settings, please consult the MT4 documentation.
The default account settings will be filled in the greyed out boxes only after you run a backtest on that symbol. This is subject to change in a future version.