e-onsoftware recommends to render in DivX codec. But you also can save your animations image by image and assemble it in another program like Quicktime. the advantage is, that, if ever your computer crashes while rendering, you don't loose all the animation. About the size: difficult to say. As big as possible, but this takes time and space. Maybe start with 360x240 renders. When you are satisfied, render bigger and when you have become an expert, you will like to have bigger anim anyhow:-)

To render an animation, click the small icon at right in the timeline. this opens the anim render options. Click advanced options to see more.

All your animations are rendered automatically inside the VueAnimations folder. Guitta