Language takes things and puts them into categories.
Imagine you are walking along a forest path and you see a fallen tree. One person might see a tree, another might see somewhere to sit, someone else might see that a squirrel calls the tree home. In reality the tree is the one thing, but through language we interpret it as several different things.
When you get home you might describe the tree to someone. To do this, you take the reality - the tree - and with language you turn it into a separate object; an object the listener can imagine, though the object he imagines might be very different from the reality.