What is a furnished apartment?
Furnished apartment includes most of the basic equipment that you require. Your rent usually includes internet & electricity. The rent is much higher, as you are also "renting" the furniture as well.
Furnished apartments are a decent solution, when you are new to Germany. You can:
Do your city registration (Anmeldung)
Rent them almost immediately, even from your home country
Easier to find than an unfurnished apartment
Although the rent is higher, it's not a guarantee to get the place if you apply. You will still be evaluated by the landlord.