Sugar-phosphate backbone is on the outside, bases in the inside. They form base pairs, which form a Hydrogen bond:

• A – T
• G – C

The Shape of DNA - Numberphile. DNA is a right-handed Helix.

Both strands are right-handed (almost always in biology) (they have to have the same handedness, as can be seen by looking at a cross-section and seeing the cross-sections of the strands, if they were of opposite handedness, they would collide (given the helices have the same radii)). The two strands of DNA also have a direction associated with them (the backbone determines it), and the strands are antiparalel, as seen in animation below

See also Chirality in biology

DNA double helix formation