Hello Alexis.
A trunk will tag frames upon egress of the frame from the trunk port. This means that if a frame comes to the trunk port on VLAN 10 for example, a tag of VLAN 10 will be added to the frame and sent out of the port. The switch on the other end will receive the frame, will examine the tag, and if the VLAN ID is in the allowed VLAN list, the frame will be accepted, the tag removed, and the frame will be forwarded to the appropriate port. If it is not in the allowed VLAN list, it will be discarded.
Now the native VLAN configuration on a trunk port simply tells the switch that if an untagged frame is received on the trunk port, it should be placed on the VLAN configured as native.
You can find out more information about this in the following post:
I hope this has been helpful!
Laz