1) This isn't an RMXP Troubleshooting related problem. This part of the forums are for actual technical aspects. That's what troubleshooting is usually for. That applies here, too.
2) You'll need to use tileset terrain tags. Set the encounter areas to specific numbers for a map. Set a variable to the hero's terrain tag. Then run conditional branches to create encounters. I don't seem to see a "set map's encounters to" thing so you'll need to make small maps that have only certain encounters.
If you REALLY need some big map or something, you'll need to use random integers for every step you take so that it calculates whether or not you ran into a battle. Then, you use conditional branches to check what terrain tag you're on and give the proper battles.
Much props to one guy (I forgot who) who said terrain tags could be used. You could allow for more customization, but that takes more variables (like different rate of encounter in different areas). I used comments to separate conditional branches, but I didn't explain everything. Hopefully you can learn from this. If you can't learn, hopefully you can at least emulate. If you can't, this kind of system isn't for you
Learn events a bit more (if ya need).