To get started with trading you need to configure a few things.
First you need to set up at least one financial instrument that you can offer your customers to invest in. Once you have created an instrument you need to have price quotes for it. You can input these manually or you can activate a feed in the add-on marketplace.
An example of how to conduct actual trading is described here: Trade Manual
One of the most important operation conducted by your back office staff is the daily reconciliations of accounts. The custody accounts owned by the house (you) should always agree with the statements from your custodians (banks and brokers) where you have your assets. By navigating to Positions in BFS and then filter on the settlement dimension, balance date, currency and account type you can see what the custody account balances per asset was in BFS for a certain date, this should then agree with your custody statements from your custodians.
Also make sure to read the article about Subscription orders where you can work with subscriptions to new instrument issues in the primary market.