There are many people that have successful 10G SW
tanks. However, they are not recommended for beginner SW
It is much easier to start with the biggest tank your budget will allow. This is because it is easier to maintain water parameters of a larger volume of water than it is for a small volume of water. Small water volumes are less stable because small shifts result in big changes to the overall water quality.
Nano tanks (20G or less) need constant supervision to ensure that the water quality is always optimal to sustain the life within the tank. As water evaporates, the salinity increases because the salts don't evaporate therefore you have a more concentrated SW
mix..... Constant freshwater top-offs are then needed to keep the salinity stable.
Fresh water top-offs are also needed in bigger tanks, but the amount of evaporation isn't as detrimental to the inhabitants because of the larger volume of water.
do a search for nano tanks on google images and you'll probably find lots of pics, but I would say that if t's your first tank, and you want a succesful tank, get something that's at least 30G+.