Quick answer:
You have to be in Vertex mode to select or adjust vertices (as opposed to entire objects). Also, you need to be sure that Vertices are set to display in your ortho windows. Orth menu > Vertices. And also 3D menu > Vertices Make sure "Vertices" is checked in each of those menus. Once in Vertex mode, click on any one vertice in an ortho window to select it, or drag a box across a group of them to select groups. Similarly, hold down the Shift key and click/drag on selected vertices to deselect them. Watch your ortho views carefully when selecting; sometimes clicking on one vertex in a view may select several other vertices "behind" it. Watch your orthos views and the red bounding box that describes the dimensions of any selection. If you're trying to select one vertice on one side of your model, but the red box is describing a much larger area, you've inadvertently selected more vertices than you thought.
More important: slooooooow doooooooown. You have to know how to navigate around the program and get familiar with how this kind of software works before you can really get to grips with creating anything. Get the .pdf manual from the Downloads page of
www.ac3d.org. Take a few hours to read the manual while you poke around the program. This will save you a LOT of aggravation in the long run.
AC3D is really easy to use, but not if you don't understand even the basics. I strongly suggest you learn the simplest things before you try to create something and get in over your head.