Just like the tittle says, I want to make a landmass mod and maybe use other people's textures and resources, what's the rules on that? And how would you use those resources without being dependent on the plugin. Sorry I'm new to modding

First, you need permission to use someone's work in you mod.
Read the ReadMe file to see if permission is given. If permission is not clearly stated, or you can't find a way to contact the modder personally to ask, then do not use that resource.
Always make a section in your ReadMe that credits whose work you have used.

To use resources, without creating dependency on the esp, you must create a new ID for the object. (make it something unique, so it won't conflict with any other mod)

- If you drag the object into the Render window before changing it's ID, the resource esp will still become a dependency. But this can be fixed with Enchanted Editor or TESAME by deleting the original resource object from your esp, (therefore just leaving your new one.)

- Change the ID before you drag the object into the Render window, and no dependencies will be created.

It's not a big deal if you accidentally create dependencies while you're working on your mod, like I said above they can be removed rather easily. Use the Preview window if you need to see an object before you drag it into the Render window.

but don't forget, you can use whatever you want, aslong as you don't RELEASE stuff without permiss.