Wings 3D is probably the simplest modelling program to get to grips with. Its generally a good idea to stick with primitives however, until your game is playable. For an island use a sphere squished on the y axis, for trees use cylinders, for rocks use blocks, for a player use a vertically tall box, etc.
If you're completely new to programming (it sounds like this is the case) then even a simple "walk around an island" program may get a little confusing to you. Sure, you might understand the code if someone gave it to you, but Id recommend reading some of the more indepth tutorials before attempting it, so you can understand how to change the code to fit your needs as well.