You will get one token when you run the docker swarm init command. That token you need to run in your worker node and it will automatically add to the swarm.
$ docker swarm init --advertise-addr 172.31.11.98
Swarm initialized: current node (v99wt041ykw5v9rfkktp7fuhy) is now a manager.
To add a worker to this swarm, run the following command:
docker swarm join --tokenxxxxxxxxxxxxxxxxxxxrnd33m7g3xfg8o0gyl1rgkxkliq8kq2ovbf2inz84bhwbdzp9ddvxrbfoi 172.31.11.98:2377
In the above example, you can see that when I ran the init command it shows me one token.