Open your project in RPG Maker MV
Create or import a gate tile or gate sprite
Place the gate on the map
Set the gate tile as impassable in the tileset settings
Add an event on the gate tile if you want it to open and close
Set the event trigger to Action Button or Player Touch
Add a switch to control whether the gate is open or closed
Use event pages to change the gate graphic when the switch is on
Set the closed page to block passage
Set the open page to allow passage
Add a sound effect if desired
Test the gate in playtest mode
Adjust passage settings and event priority if needed