(http://i.imgur.com/1M290O9.png)
The first part for making a patch, involves creating a brush. Select the brush, and then, based on how you want to move on, you do either of these:
It's important to note, that the side of your brush that is displayed in the 2d-view, is the side that will turn itself into a patch. This applies to Curve & Terrain patches. You can always rotate the patches if they're not oriented correctly.
Marked with 1, a simple curve patch is made when you want fine curves. An archway, a nice bend around a corner, or anything you can think of, a curve patch can be used to.
(http://i.imgur.com/wx8PkLj.png)
The first thing you're presented with when selecting Simple Curve Patch is the options for how many verts you want in the patch. Pretty self explanatory, you choose how many verts you want on the vertical and horizontal part of your patch. A simple 3x3 will give you a total of 9 verts. Simple Math, yes?
Here is an example of how you can use a Curve Patch to get a smooth curve, for example when creating a hangar.
(http://i.imgur.com/fvwobUZ.png)
Marked with 2, a simple terrain patch is made when you want to work with terrain, or work with blends. Terrain with different levels of elevation on different parts of the patch, blending out a texture to add more detailing, and more.
Just as with a curve patch, you're firstly presented with the option to select how many verts you wish to add into your patch. It's a simple multiplication, having 2 in width and 2 in height gives you a total of 4 verts. In this example, that would be each corner.
(http://i.imgur.com/TJ72fTi.png)
Here is an example of how a Terrain Patch can be used to make a blend:
(http://i.imgur.com/UH2PGZi.png)
Marked with 3, primitives are mostly cylinders, but also offer for bevels, and bevel-caps. Water tanks, pillars, pipes, anything that might require some round parts.
There are multiple options inside Primitives, although Cylinders tends to be the main reason to visit this part.
(http://i.imgur.com/clqjW7W.png)
Playing around with the different options here can give you different shapes. Just like a Curve & Terrain patch, it comes with verts.
Here is an example of how a cylinder can be used to produce pipes. You can also create pillars, and similar structural features using cylinders:
(http://i.imgur.com/w9aFYHR.png)
Moving & Editing PatchesIf your patch is positioned correctly, and/or you want to flip which side of the patch is displaying a texture, CTRL + I will alternate inbetween both sides.
To enter vert-editing mode, simply hit V when a patch is selected.
To add more verts, select two verts on the same axis of the patch, and press CTRL + A
To select a vert on your patch, simply drag-select with the mouse. When you're in vert-editing mode, Radiant will switch to a drag tool, so just drag your mouse over the verts you want to select. Re-selecting an already selected vert will deselect it. It's worth noting that when you try to select more verts, the previously selected verts will be deselected. To prevent this, simply hold down CTRL while you select your verts.
(http://i.imgur.com/NEt3mzf.png)
When you want to move a vert, you want to hold down ALT, and use Right Mouse Button to drag the verts. Switching between all 3 view in the 2d view, you can easily move it in all directions; x,y & z.
If a vert is not in place, CTRL + G will move the vert into it's closest location on the grid, so depending on how fine tuned you have the grid at the time, the movement for the verts may change.