red ring of death

Never use that towel trick, it overheats everything in the box, including fragile capacitors and ICs.

Here is the overall summary to repairing a RRoD. Underneath the GPU (graphics chip) there is something called a Ball Grid Array. These are connections between the chip and the motherboard, and through heating and cooling, along with a design flaw in the 360, these balls can crack or become slightly dislodged.

Since you are a beginner, I will overview the simplest fix, the X-Clamp Replacement. The other two methods which are better (A Wave Station Reflow and a Reball), are very advanced.

You'll need T10, T8 Torx drivers, 16 M5 (Metric 5mm diameter) bolts, 1mm M5 steel washers, 8 M5 1mm nylon washers, a 13/64" drill bit, and some thermal grease.

After removing the motherboard, you'll need to take off the GPU heatsink (the flat one). There are four friction-bolts on the heatsink that need to be removed with pliers. You'll need to drill 13/64" holes through the old T8 holes that held down the heatsinks. M5 bolts go through the holes, 3 steel washers, 1 nylon (to isolate the motherboard). Motherboard goes over the bolts, then 1 nylon against the mobo, one steel on top of it, and screw the M5 bolts into the heatsink. Tighten the M5 bolts fairly tight, a little more than finger tight, but not excessively or you'll crack the motherboard.

You'll need to overheat the GPU (and only the GPU), by placing in the DVD drive, removing fans from their housing, and sticking them on top of the DVD drive so one fan is pointing down into the CPU. The temperature sensor for powering down the system in excessive overheating is in the CPU, so this way only the GPU heats. The excess heat will "sweat" the BGA, and after about 45 minutes of overheating, turn off the system, don't touch it for 20 minutes, turn it on, should be fixed.

The penny trick is absolutely worthless (it does nothing, in any way). The towel trick is 'very' temporary, and damages other components. Either use an X-Clamp replacement, a Hybrid mount, a Reflow, or a Reball.

Do your own research, there is a TON of information on how to solve this. YouTube will only mislead you, google is your friend, try Xbox-Scene, Xbox Hacker, or hop into EFNet and be friendly.