Why wont my 1996 geo metro auto trany shift into first gear when put into drive?

Your 1996 Geo Metro's automatic transmission may not shift into first gear due to several potential issues, such as low Transmission Fluid levels, a faulty transmission solenoid, or a malfunctioning throttle position sensor. Additionally, a clogged filter or internal transmission damage could also prevent proper shifting. It's best to check the fluid level and condition first, and then consider having a professional inspect the transmission for more complex issues.