Welding is like using glue but instead of sticky goo, you use heat to join two things together. The heat is really hot, like when you hold your hand over a candle, so you have to wear special gloves and a mask to protect yourself. You also need a special machine called a welder that uses electricity to make the heat.
When you weld, you have to make sure the two things you want to join together are clean and touching each other really well. Then you hold the welder near the spot where you want the two things to stick together. The heat from the welder makes the metal melt and become soft so it can stick together. It's like melting chocolate so it sticks to your fingers, but the metal is much harder to melt.
After the metal cools down, it becomes really strong and hard to break apart. Many important things are made by welding, like bridges, buildings, and even cars. So, welding is like making things stick together with really hot glue that is made by a special machine called a welder.