Why is my car not showing the lights for the gas and speed mileage?

bad fuse, broken wire, blown bulbs, or loss nut behind the wheel!

Check your fuses and if they are okay your panel lights have gone which can be a pain to replace on modern cars so best left to a mechanic. The dashboard will have to be removed to gain access. Not a DIY job unless you're a real handyman. 

Get out your owners manual, read what fuses cover those lights, look at the fusebox diagram, find what fuse or fuses those are, and then open up the fusebox and look to see if they're burned out. Replace and test.

The bulbs in the instrument cluster need to be replaced.

Please explain - what is the "speed mileage" light?

First check the light control, it may be turned off (directions are in the owners manual), if it is on then check the fuse (information on this is also in the owners manual). If the fuse is good then it might be the bulbs. Often not easy to get to and requires taking the dash apart to get to the bulbs. Check U-tube on this one.

Either a fuse or a light has burned out.