Answer
Hi,
In the allegory of the cave Plato tries to tell us that human can think, speak and do a lot of other things with no awareness of true realm of these forms.
Step-by-step explanation
In the allegory of the cave the prisoners can only see and hear shadows and echoes produced by objects which are invisible to them. In this case, they can mistake appearance for reality. This is to mean they will take the shadows to be real not knowing real causes of those shadows. The meaning is that terms used in our language are not names of physical objects that we see but names of things we can not see, but only grasp with our minds.
Hope this helps!