One time when I was playing MvM with my friends, one of them said for all of us to switch to Engineer and put down lv3 sentries all over and it was my first time playing as someone other than Pyro so I didn't know how his things worked so after they told me which one was the one used to put down sentries I asked them how to put down those things, yeah?? Well whenever I pressed F1 it didn't do anything so I was basically running around with this big as heck toolbox and fREAKING OUT LIKE A DUMB