If I want to play guitar just for me because I like it, is it Haram or Halal?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Using the guitar is not permissible since it is among musical instruments that are forbidden. All the Muslim scholars are agreed upon this fact.
For more details, please read the Fatwa: 81239 and 81545.
Allah knows best.