I am fairly new to Creation Kit. I've been working on a mod that past 2 weeks now, I've made a new WorldSpace set apart from normal Skyrim.
My problem is that my enemies can not move, due to not having navmeshes put down.
So I have started doing them only to realize that there are certain areas where they can not connect.
For example;

I would be in ' Wilderness ', and then it would not connect to the next ' Wilderness ' ( sorry if that doesn't make much sense, I'm hoping you understand what I mean )

Can anyone tell me what it is I'm doing wrong? Why can't they connect between the two?

There will be green lines (borders) between one exterior cell to the next once you get it navmeshed and finalized. It's tricky sometimes, but you have to line your verts up to match each other on either side of the border. YOu can hit you "B" key to see where the borders should be. From the wiki: "Make sure to Finalize your Navmesh. In order for exterior Navmeshes to finalize correctly, the verts on the borders of each cell must be aligned with corresponding verts in the adjacent cell. A green edge indicates that a connection has been made."

Basically, navmesh one side and all out verts should not be able to cross the border. Then start on the other side, and line verts up on that side to match the first side.

Do you have a link to a video that might demonstrates this?

Don't really know of one. It's pretty simple though. Try placing a vert next to a border and then try to move it across the border. It will stop on the border line and you can't drag the vert across the other side of where the border is. So, add 2 more verts and make your triangle. When you place your verts and triangles along the border, just hop over to the other side of the border and add a vert. Then pick a vert on your other side and line the new vert op basically in top or inside of the vert on the other side of the border. You're really only matching up your verts on each side of the border. Take a look at any vanilla cell, pull up the navmesh and zoom in on the verts along the border. They're basically sitting inside each other. Make you a test or junk plugin that you don't care about dirty edits and pull up an exterior cell and drag some verts on the border around and you'll see what I'm talking about.

Nevermind! I got the hang of it immediately after I asked for a link, lol.
Thanks though! I didn't know there was an actual Finalizing thing.