I have sewn a lot of leather by hand and by machine, so let me help you. First of all, you have to have a walking foot industrial or heavy duty machine to machine sew nand really heavy needles, size 16 or 18, and I used nylon thread called nymo.
By hand you need leather or glover's needles, they are three sided on the tip and very sharp, available at someplace like Tandy Leather or in some craft needle selections. You can use nymo thread which has a twisted ply or heavy cotton or polyester. If the leather is cowhide, you may need a sewing awl, which may have that type of needle already. Without the awl or the right needle, it is next to impossible to get a needle through the leather. If it is elk, or something softer like that, it is easier to sew. If you make a mistake, the hole will be there forever. I would not try it if the person is picky. Leather is fun, but a whole new game in sewing. Hope this helps.