A Gateway exposes other devices to the AllThingsTalk cloud. They are useful when dealing with devices which cannot connect to the cloud on their own, or when those devices are using protocols which are incompatible with the ones AllThingsTalk uses.
You can use gateways to bridge the gap to various low-power protocols, such as Bluetooth, as well as various LPWAN implementations, like LoRa and NB-IoT.
It should be noted that if your product supports TCP/IP stack, gateway might not be required, and it will be simpler to implement your product as a standalone Device. However, there are some instances where gateway should be used, for
To create a gateway in Maker:
You can use REST/HTTP(S) Gateways API to develop clients that manage network of devices, their assets and state.
Read API reference docs here