LEGO trains come with special wheels, wheel-bases and magnetic connectors that are only available with LEGO train sets. While you might be able to cobble together something that sort of works, there is no substitute for the actual train parts.
The train wheels are designed in such a way that they can run smoothly on both curved and straight LEGO train tracks. If you study their shapes, you will see that they are actually quite complex. Train wheels are connected with small metal rods, instead of LEGO Technic axles, to assure a very smooth ride over the tracks. The special wheel-bases are designed to accommodate the wheels and metal axles, and are just the right length to be able to handle curved tracks. And the magnetic connectors allow easy coupling of the train cars.
While some LEGO car wheels have grooves, they are not designed to fit on LEGO train tracks. Some can sort of perch on top of the rails, but they are wobbly, and will run off the tracks easily, especially on curves.
If you would like to get into LEGO trains, I recommend getting an actual LEGO train set to avoid all the hassle and frustration of trying to build something from parts that are not meant for trains. Just get the cheapest LEGO train you can find. It will give you all the parts you need to build a train, and you can always customize the engine and cars from parts you already have.
Currently, the cheapest LEGO train is the #75955 Hogwarts Express for $80. However, you can often find better prices on eBay for used LEGO trains or partial sets with only the train but no extra parts and minifigures. Also check Amazon during the holiday shopping season. They usually discount older LEGO trains by 20-30%.