If you're gonna get into 3D modeling, an iPad probably isn't going to cut it. It's simply far too complicated for a touch screen device and you need an actual keyboard. Plus rendering is hard on systems, hand held devices likely don't have the processing power needed
Like onessu said, Blender is free and the tutorial they're following is a great start. Plus it has a huge community with so many tutorials and resources, so you'll have plenty of help whenever you need it. I use Blender myself and love it. 3D modelling is very confusing and tricky at first though, so be patient with yourself and start small. You'll get the hang of it eventually, just keep practicing and trying new things~