Starter, Booster or Random Booster? What is actually in the box
Starter — the blade and a launcher
Takara Tomy lists the Starter as the place to begin, and gives its contents as the Beyblade itself plus a launcher. That is what makes a Starter the only one of the three that is playable on its own, and it is why a Starter costs more than a Booster of the same blade.
What a Starter still does not include is a stadium. You can launch into a bowl or onto a hard floor, but the battle rules assume a stadium, and a blade launched onto tile chips its own bit.
Booster — the blade only
A Booster is a complete blade with no launcher in the box. Takara Tomy prints the consequence on the product page: to play with it you need the series' own stadium and launcher, sold separately. So a Booster is the right buy once, and only once, there is already a launcher in the house.
This is the single most common mistake in a first Beyblade order — a Booster is cheaper, looks identical in a photo, and arrives unplayable. If you are not sure which you are looking at, the word is printed on the front of the box.
Random Booster — a blade, but not a chosen one
A Random Booster contains one blade out of a fixed assortment, and you do not know which until it is open. BX-14, the first one, held one of six types: one designated rare, and the rest special-colour versions of blades that already existed. Later Random Boosters follow the same shape, with the assortment and the rare named on the box.
A Random Booster still has no launcher, exactly like an ordinary Booster. Buy one to chase a rare or to add colourways; do not buy one expecting a particular blade, and do not buy one as a first purchase.
The other thing worth knowing as a buyer: a listing described as "confirmed" or "opened" from a Random Booster is a single blade someone has already pulled and identified. That removes the lottery, which is usually why it is priced differently from the sealed box.
What a complete first set-up needs
Takara Tomy's own answer is the set: its example lists one Beyblade, one launcher, one launcher grip and one stadium. That is the full kit, and buying it as one box is cheaper than assembling it from a Starter plus the gear.
To play you set the blade into its dedicated launcher and shoot on the "3, 2, 1, Go Shoot" call. A battle is first to four points, scored four different ways, so two blades and one stadium is a real game — a second Starter, or one Starter and one Booster, is the usual second purchase.