The mRNA is complementary copy of the DNA gene but consists of uracil in place of thymine in the sequence.
mRNA is made of DNA by the process of transcription. The part of DNA is transcribed into mRNA in 5' to 3 direction. It happens because it follows the central dogma for molecular biology which states" the genetic information flows DNA to protein product in a framework".
DNA→RNA→Protein(central dogma)