TNT in Minecraft Bedrock is crafted using five units of sand and four units of gunpowder, arranged in a cross shape in the crafting grid. It can be activated through various methods, resulting in significant explosions. Custom TNT allows players to create unique explosions using command blocks, redstone mechanics, and innovative designs like TNT cannons and traps. Advanced techniques include mastering redstone circuits, TNT duplication, and utilizing data packs for further customization. Safety measures are essential when testing custom TNT, including using a controlled environment, protective gear, and regular backups of the game world. Common issues include TNT not exploding, unexpected explosion effects, and lag, which can be resolved by checking redstone circuits, adjusting parameters, and limiting the number of TNT blocks used.