I'm not on the GFX Team or a Pro at GFX but I can surely give some advice.
Times like these the 'GFX Resources' & 'GFX Tutorial' Sections come in handy.
Secondly, if you want to use an apple device and own a Apple Tablet; like iPad Pro, Mini etc. And you have money to spare; I recommend getting the stylus or the Pen they came out with. There are some really nice apps that will help you achieve just that. (And no, it won't work with your Fingers)
On the other hand, if you don't want to spend money You need a PC. An average PC that runs stuff smoothly and somewhere you can Pirate. Then there's a wide range of Softwares that are available that will also help you do GFX. Not just Drawing, Manipulating, Enchancing etc. But much more.