You will always start the game in any mode in Halo Infinite with the starting equipment. It will usually be an ordinary assault rifle, which is best suited for medium distances. During the game, there will be many situations in which you will be able to change weapons – usually, guns lying in special boxes have better statistics than the starting one.
If you want to change weapons, go to the shelf (usually they look like the one above) and hold down the appropriate button for your hero to pick up another weapon. The same applies to rifles dropped by players or dropped in special boxes.
Remember, however, that the gun he is currently holding will be replaced with the new one – if you do not want to get rid of, for example, the starting assault rifle, turn the mouse wheel to select the second weapon slot. By default, you will find a pistol in it that you can easily exchange for any type of gun.