Translation:There is a small carpet on the floor.
This one works pretty much like "there is" in English. One reason the language has these constructions is because of word order. For the information structure to work well, it's much better not to start a sentence with an indeterminate noun like "en matta" or "en mus": these items are unfamiliar to the listener so having them as a subject of the sentence feels unexpected. What you want to tell the listener is of the existence or presence of something. Therefore, you want to have the verb before the subject. But we can't just put the verb first, so we need a construction like this.