This is the SST v1 Constructs doc. If you are using v0.x, see the Constructs doc here.
Constructs are the basic building blocks of SST apps. Each construct consists of multiple AWS resources to make up a functional unit. SST picks sensible defaults for the underlying resources, so you are not exposed to all the complexity up front.
Here's a rough list of the types of contructs that SST supports.