Sometimes you need something a little stronger than a regular gun, and that's when you remember that you can throw grenades at your enemies in Borderlands 3. You even have a grenade modification slot that allows you to customize exactly what type of grenades you want to use, as well as their damage.
Throwing grenades is bound to a default key on your controller or keyboard, and the following is the default button for throwing grenades:
Xbox One: RB.
You can of course bind it to another key from your settings, but this default key should work if you just forgot how to throw grenades in Borderlands 3.
It can be a bit tricky to aim the grenades exactly where you want them to land, but remember that they will always be thrown towards the centre of your screen where the crosshairs are. However, gravity and other things will affect them, so it takes a bit of practice to get it to land exactly where you want it to land.