I've been asked too many times so here is an in-depth explanation of 2-4-6-8 law.
A large scale view of 2-4-6-8
And now for the guide:
1: You start with your 'dirt paths'. IE this is your frame. Since frames are pushed 2, 4, 6, or 8 times, you can build stairs, whatever on the frame without it screwing up cubes due to incorrect gridsize. Frames are always pushed an EVEN number.
2: keep your frames square. Generally, one part of the frame shouldn't stick out farther than another, all 4 sticks of the frame should meet together, as shown below.
3: Building more frames, I will only use 2 frames for this guide.
4: Now, you simply fill in your frame, working from corners to center.
5:
6: (optional) - sometimes there are situations like this. You can push it inwards up to 4 times. (you can go more.. but it might not look good.)
7:
8: Now take the bottom part, and push it 2-4 times.
9:
10: Flip and push it til it matches. (if it matches after 2 pushes, push it 6 times. If it matches at 4, push 4. If it matches at 6, push 2.
11:
12: Then flip it back in place.
13: Same kind of thing here, generally.
14:
15:
16:
17: Progress.
18: Finished with frame.
19: Then just go through, and do some touch-up for the frame. (IE smooth it all out.)
20: Now for dirt paths, assuming you will be making them actual paths for playable map.
Build some stairs, or whatever really. It'll fit. Just make sure to match it for the slope.
21: Go ahead and make your 'base, default' method of travel. In this case I used wooden stairs.
22: Select a 'slope'. This slope is a 4 slope, it has been pushed down 4 times (center) 8 times (right side). Copy paste it on available empty place in map.
23:
24: make your uh, post, on the FIRST cube of the slope.
25: make your uh, connector majigs.
26: There you go, copy paste it to the other side of the slope so it matches.
27:
28: Now go ahead and do that for all the slopes. You really only need to do it once for each slope type, you can copy/paste/rotate it to fit onto other slopes.
29: Then just add some detail to it, whether it be mapmodels, blendmap, whatever.
And you're done with your terrain.
Amount of time to make actual map for guide: like 15mins
Amount of time to upload pics to imgur, and make this guide, like 20-30mins
Total time to make guide: bout an hour.
Map included below.