"That is the garden."
Translation:Sin an gàrradh.
There are two verbs to be: "tha (bi)" and "is". "Tha" is mostly for describing things, but "is" is like putting an equals sign between things - it says what they inherently are.
The trick here is that in some situations (with sin and seo particularly) "is" itself can be left out, so this is really either "is sin an gàrradh" or "is e sin an gàrradh".