A starter bundle is one order that moves a fresh or neglected account onto a footing where it is playable with everyone else. Each tier lists its contents in full above: which class tracks get raised and how far, which weapons, armor and equipment are delivered, which vehicles come with it, and how much in-game cash is included.
It is built for the account that is behind on everything at once rather than short of one specific thing. Buying the same contents as separate leveling, cash and item orders costs more than the bundle does, which is the only reason bundles exist as a product. If you are short of exactly one unlock, a single item drop is the cheaper order.
The tiers are cumulative: each one contains what the tier below it does and adds to it. Read the feature list on each card rather than the tier name, because the difference between two neighbouring tiers is usually one class track and a vehicle, and that may or may not be the thing you care about.
You can add in-game cash on top of any tier from the same panel, which is the common adjustment: a lower tier plus the cash to buy your own choices often beats a higher tier that picks them for you. The total updates live as you change the tier or the cash amount, and that total is what you pay.
A bundle is delivered on your account, so we need a login. It is encrypted at rest, readable only by the assigned booster, access logged, and deleted when the order closes. Disable anything that would lock a booster out part way through, and tell us your usual region so sessions come from where your account has always played.
A bundle is delivered in pieces, and the refund rules follow the pieces. If a tier is part delivered and then stalls past the agreed window, you are refunded for the lines that were not delivered rather than being offered store credit. Every completed line is recorded against your order, so what is owed is a matter of record and not of who argues harder.