The term "Quantity" at Broker AGEA

@ dartz:
- … what percentage of the capital should I use for Quantity …

Perhaps you mean risk that is set.
Setting the amount of risk in money management does not depend on the size of the capital. Usually between 3% to 5% of capital or equity, which is the value of the stop loss (SL).
After that, set the size of the SL in pips, so that the volume (lot size) for entry is known. This method is called position sizing.

For more information, please read:

• Learning to Understand Money Management
• Money Management Strategies With Position Sizing