After i changed the cotton, i applied some juice on it and the coil then i burned it. My question is, when im burning it the coil was not supposed to turn red as if it was heated right?
If you are trying to Clean the Coil by applying Power to it, we call that "Dry Burning".
Here are the Steps most people use to do it...
1 - REMOVE the Wick.
2 - Rinse the RBA/Coil with Warm Tap Water.
3 - Blow and Shake the RBA/Coil to get it Dry.
4 - Set you Mod to a Low Watts, 8 Watts or so.
5 - Connect the RBA to the Base and then to the Mod.
6 - Push the Power Button for 2 Seconds or So. Then Let Off. Keep Doing until No Smoke comes off the Coil. You Don't have to make the Coil shine Red constantly. But if it does so Briefly, that is OK.
7 - Let the RBA / Coil cool for a moment or so.
8 - Rinse the RBA/Coil with Warm Tap Water.
9 - Blow and Shake the RBA/Coil to get it Dry.
10 - Rewick the Coil.
11 - Prime the Coil/Wick with a Few Drops of e-Liquid.
12 - Reassemble everything. Fill the Tank. Take few hits without Inhaling.
13 - Raise Watts back to what you Normally vape it and you are Ready to Go.
ETA: NEVER Attempt to do this type of Dry Burning when there is a Wick in the Coil !!!