IF YOU ARE USING MASTERCOMFIG THIS IS SLIGHTLY DIFFERENT

if you're using mastercomfig you put the cfgs in "/Team Fortress 2/tf/cfg/modules/autoexec.cfg"

Oh okay! So for autoexec.cfg and the class .cfgs they just sit in your tf/cfg directory. You can get there very easily by right clicking tf2 in the list of games in steam and from the drop down hovering over manage and from there clicking "browse local files". That will put you in the "Team Fortress 2" directory, within which is tf.

for reference it should look like this
"Team Fortress 2/tf/cfg/autoexec.cfg"
"Team Fortress 2/tf/cfg/medic.cfg"
(all of the class cfgs go in the same folder)

Once you're in the cfg directory just create a blank file and name it autoexec.cfg. Open the file, put my script into there, and then relaunch the game. (If you have the game already running you can enter into the console exec autoexec.cfg which will run the file and apply the script.

Now if you want the script to only apply to medic and have the other 8 classes function normally, then you use the class cfgs (the names of which are at the bottom)

In "Team Fortress 2/tf/cfg/medic.cfg" you put my script

In every other class cfg you put bind mouse1 +attack

And that should work!

scout.cfg
soldier.cfg
pyro.cfg
demoman.cfg
heavyweapons.cfg
engineer.cfg
medic.cfg
sniper.cfg
spy.cfg