Your clan castle is your best defensive structure even though it is not classified as such, but only when it has donated troops inside it.
You have 10 spaces that means two people can donate archers to you.
Even if they only donate lvl 1 archers at 7 DPS each that's 70 damage per second in the one building, vastly stronger than any other defensive building.
Placement of the clan castle is important, at the early stages you want to place it so it has 100% coverage of your base that way an attack from any side will trigger it.
All the more reason to find a good active clan (check the clan talk part of our forum for that)
There is a tutorial here on the early days that might be of help for you.
https://www.youtube.com/watch?v=bzyX...lXQucULU3TpzoV