The Tutorial is pretty straight forward. Use scroll wheel to move a prop away or toward you and right click to nail it down. Afterwards before leaving the level interact with the merchant and purchase a rifle and complete the first three rounds of the shooting range. 3/7 achievements already done.

Sure you could barricade yourself inside or try to kite the zombies, but that takes a lot of effort. Instead go inside from the door nearest the merchant on either Onslaught or Survival and look to the left. There's a spot you can use props to get on top of that the zombies can't reach. For good measure I picked up a chair and put it on top and stood there. Have fun killing zombies :) Just make sure to press o to advance the wave when you're ready, just like it says on screen.