Yes, they are real but they don't run around showing themselves to humans because are angels who followed Satan in rebellion against God (Revelation 12:3–4). The Bible doesn’t give many details about demons, but what it provides is enough to dispel typical myths.
Demons are referred to by several alternate names, including “unclean spirits” and “evil spirits.” Some of the false gods that received human sacrifices are described as actual demons (2 Chronicles 11:15; Deuteronomy 32:17). Since demons are fallen angels, they possess the same level of power and influence as angels. However, Scripture seems to indicate that God has limited their abilities (2 Thessalonians 2:6–7). The Bible indicates that not all afflictions are due to demonic influence (Matthew 10:1; Luke 8:2). The vast majority of demonic influence is spiritual, not physical.
Popular culture frequently depicts demons in monstrous form. This includes drooling fangs, sharp claws, leathery wings, and so forth. Or they are portrayed as shadows or ghosts. None of these have any biblical basis at all. In fact, the Bible never physically describes any fallen angel. As is the case with angels, demons are spiritual creatures with a primarily spiritual influence, so they are unlikely to have any set physical appearance. If they choose to take on a physical appearance, it actually makes more sense for them to choose something inviting rather than scary (2 Corinthians 11:14).
So, demons are literal, actual beings. The demons described in the Bible exist. However, the oft-portrayed horror-movie and Halloween versions do not.