SSH into the first node via vagrant ssh, then call this to initialize it as the first node in the Swarm:
sudo docker swarm init --advertise-addr 192.168.2.3
sudo docker swarm join-token manager
Copy the command you got from calling docker swarm join-token and run it on node2. Then, on node2, run:
cd /vagrant
sudo docker stack deploy --compose-file ./docker-compose.yml web
This will start a .NET Core MVC web application that can be accesses at 192.168.2.3:8080 or 192.168.2.4:8080.