You can use the CreateThingType command to create a thing type:
$ aws iot create-thing-type --thing-type-name "LightBulb" --thing-type-properties "thingTypeDescription=light bulb type, searchableAttributes=wattage,model"
The CreateThingType command returns a response that contains the thing type and its ARN:
{
"thingTypeName": "LightBulb",
"thingTypeId": "df9c2d8c-894d-46a9-8192-9068d01b2886",
"thingTypeArn": "arn:aws:iot:us-west-2:123456789012:thingtype/LightBulb"
}