Resources can be used to add functionality to your FiveM server, you can find many of the available resources in the Releases section.
Some may be free and others may not, the forum has filtering functionality so you can sort through them.
Use at your own risk. Resources are community driven and you should pick them carefully. FiveM is not responsible for any event following its use, and will not provide support for community made resources. Make sure to follow the resource terms and conditions. Resources generally have a way to communicate with the creator for support, use the available lines in the event an issue arises.