Betty, Sierra Leone is one of the poorest nations on earth and until a decade ago was riven by an atrocious civil war. Economic development is only just starting to show gains. Where poverty exists, so do high levels of crime, especially petty crime.
One other very special thing to consider.... most flights arrive in the evening and the road from the airport is notoriously dangerous. As are the ferries which run across the wide estuary from the airport to Freetown. It is highly recommended that you do not attempt this journey at night... book an airport hotel room (limiteed availability, so book early) and do the trip during the day.
There's more about this warning here:
Phil from the safety hub about 6 years ago