hey
@Jie in order to make a public warp, you want to do the following...
- do /is and find the island you want to create the warp on
- right click to manage the island
- click island warps (ender pearl)
- move your player to the position you want the public warp to be
- click the emerald block to create a new warp
- right click the warp you just created to manage it (ender pearl)
- then click the sign labeled 'click to show this warp on /pwarps'
From here you can do a number of other things like change the item displayed on /pwarps, move the warp, change the category of the warp, or rename it.
Please let me know if this helps!