Trash in computing is like a big box where you can put things that you don't really need or want anymore. Just like when you clean up your toys and put them away in a toy box, on your computer, you can select some files or documents and put them in the Trash.
But, just putting something in the Trash doesn't really delete it forever. It's like when you put a toy in the toy box, it doesn't mean it's gone forever. In order to actually delete something from your computer, you have to empty the Trash box.
Sometimes, you might accidentally put something in the Trash or maybe you weren't sure if you wanted to keep something or not, so you deleted it but later realized you actually need it. In that case, you can still get it back from the Trash box, just like how you can take a toy out of the toy box if you change your mind.
So, the Trash box is just a place where you can put things you don't want anymore, but you can always change your mind and get them back if you need to. And when you're sure you don't want something anymore, you have to empty the Trash box to delete it forever.