Best displayed in Conquest, as a squad leader you'll be earning points and these can be used to give your team benefits throughout matches. As the match progresses your squad in general will be earning points alongside you. You'll see this point system beside your name at the bottom left of the screen.
It'll prompt you to hold LB + RB to present a new wheel that gives item options. The most basic selection and the cheapest is the "Supply Canister Drop" for 2450 points. If you do this twice you'll unlock the "Call ’em in!" Achievement/Trophy as well. That has to be completed within a round/match though. That aside, you select the item/vehicle from the menu and you're given binoculars.
You then find a clear spot and call them in, your squad will be shown what's happening and can jump in on the bonuses. For context you become the squad leader by matchmaking as the party host, starting your own squad while in a game or just waiting until someone leaves to be promoted. You can also get kicked out of the position if you're not actively engaging in the action.
Hope this helps out with the whole reinforcements aspect of the game, it can be really great when used well. Save those points up and get ready to unleash them upon the enemy in the form of weapons. With that, read about the install size of the game below or view the hub for further coverage on the title as well as the franchise in general.
Read our Battlefield V Install Size
View our Battlefield Hub