In Eve Online, when you get a newly fitted ship (or you switch out your weapons) you will want to regroup your weapons.
Here is a super quick YouTube video showing how to group your weapons once you undock your ship from a station.
There are, of course, occasions where you may want to take 1 weapon out of your grouping. This will generally happen in pvp fleets where your ship doesn’t have any EWAR (webs, scram or point) and you want to get in on a pod kill. Make certain your FC is ok with you using 1 gun, missal launcher, rocket launcher or torpedo launcher to do a little damage first!
Have fun and fly safe!