When naming an organic molecule with a double bond, the chain has to include the double bond. This means that there are 8 carbon atoms on the central chain. The molecule is octene. The double bond is after the second carbon, making it 2-octene. You can't say that its 6-octene because you want to have the smallest number possible in front.
The molecules attached are two methyl groups. Since you have two methyl groups, the name will be dimethyl. Start counting from the side closest to the double bond. This gives you a 3, 5-dimethyl group.
