This is like the 5th post about this same thing. Please try to keep your posts to one and also use the search function as mentioned in your MANY other threads on the exact same subjects.
To answer your question, at least in this thread:
You can mount with tooth pics, plant wire, etc. Put a little loose sphagnum moss around them depending on the plant. Thats how you get them on the backgrounds. Also depends on background. I use clay and can grow plants right on it.
You need to research what type of soil you are going to use. Cant just buy topsoil and be good to go. Needs to have a specific drainage. Also need to avoid anything with chemicals. Being new I recommend you buy a prebuilt package from one of the sponsors here. ABG mix is a good one. Also will need leaf litter.