Problem with mirroring.

Hey, guys I’m new to Blender and I’m having trouble making a symetric hand for a basic character I’m doing. I try to use the mirror modifier but it automatically merges itself.

Copy-paste . I don’t want that.

Mirror modifier is broken.

The mirror modifier by default mirrors about the object origin (orange dot in your model) not the world origin.
Either move the object origin to the world origin or in the modifier settings select an object in the ‘Mirror Object’ box that has its origin in the correct location such as the body object. If the body has a mirror modifier you could also just joint the hand to the body (Ctrl+J)