Recycling is about reusing something so that it does not have to go into a landfill.
When you make something, you very often do not change the materials. For example, when you make a chair out of wood, the wood has not been altered. But it will have been cut into a variety of shapes, and this makes it more difficult to use in the future. However, it can still be reused, perhaps by making it into chips that can be used to make woodchip panels that can be used for kitchen worktops.
When people make a plastic object, it will most likely have been made from oil. It cannot be made into oil again. But many plastics can be reused just by heating them until they go soft. The plastic may have printing all over it, so when it is time for recycling, the range of items you can make with it are smaller. But it can be chopped up into chips, then heated with a dye. This dye will cover up the printing. Then it can be reused as, for example, road safety cones or flowerpots.
When you make something out of glass, you combine a number of materials, and they cannot be separated again. However, glass, like many plastics, can be reused. It is simply a matter of heating it until it melts, then recasting it into something new. Again, if the glass has been coloured when it was first made, then that colour has to be disguised in some way. As before this is often done by using a stronger colour. Or you can just accept the slight colour in the glass and make it into new objects that have a slightly coloured tinge because this can be attractive. The video shows recycled glass that has a slight green tinge, but it actually makes it more attractive.
Another thing that can be done with glass is to grind it up into small pieces. It can then be mixed with tarmac and used to make safety strips on roads. The glass is used to make the tarmac rougher.
You can recycle metals in much the same way. Automobiles are stripped down at the ends of their first lives and crushed, then taken back to steel works where they are melted down. The melting gets rid of any colour, and impurities float away, so you can get new steel from old without any loss of quality. The same is true of aluminium, copper and many other metals.
So, as you can see, it is possible to recycle many of the things we use. But why should we do it? The answer is that the Earth has limited amounts of oil, metal and many other materials, so if we don't reuse them, we will run out of them. It also uses less energy to reheat and melt metals than it does to get them out of rocks in the first place, so recycling is often a cheaper thing to do as well.
