Two carbons contribute 8 and six hydrogens contribute 6.
Connect the carbon atoms.
Start with a C–C single bond.
Attach three hydrogens to each carbon.
This creates six C–H bonds.
Check the electron total.
Seven single bonds use all 14 electrons.
Verify octets and charges.
Each carbon has four bonds and every formal charge is zero.
Why there is no double bond
Each carbon already has four single bonds: three C–H bonds and one C–C bond. Adding a double bond would give carbon five bonds and exceed its usual octet.
Geometry
Each carbon has four bonding domains, so the local geometry is tetrahedral. The flat Lewis diagram does not show rotation around the C–C bond.
Common mistakes
Drawing a C=C double bond while keeping six hydrogens.
Putting a lone pair on carbon.
Calling the entire molecule planar because the Lewis formula is drawn on a flat page.