This link explains more about the order execution. Order Execution policy
Due to the inherent nature of a moving market and any delays in displaying information through our mobile application, it is likely that the actual execution price will differ from that shown on screen before the order is made.
You should be conscious to accept the risk associated with this type of instruction. Freetrade will not be liable for losses incurred due to the selection of the Instant Order type, save any assessment made by us that we have fallen short of our best execution obligations.
You should also familiarise yourself with bid/ask if you aren’t already. If not here is a good link Bid-Ask Spread Definition
I hope this helps and happy investing