Render to texture is what it says it is: It uses a texture as framebuffer to render the scene on it. The texture itself gets rendered into another framebuffer, usually the one that is also used to render all the other things into and then gets flushed on the screen. This can be useful to post-process a scene. Just render everything in a texture, manipulate it and then render the texture on "the screen".

Isometric rendering is rendering a scene with an parallel matrix. This takes the depth out of the scene and makes everything look like 2D.