These stay on the Battlefield after you cast them, and can attack other players directly (hitting the other players to lower their life total) or they can block the attacks of other creatures (take the damage instead of you, and going into your graveyard if the damage taken in one turn is greater than their toughness)
Mono-colored Commander decks aren't overly common, but there's an argument to be made that Red is the best color for building such a deck
The spells you're going to want the most are what are called "removal spells"these are the spells that permanently neutralize your opponent's creatures by either dealing damage, keeping them tapped, or just straight up destroying them
The headliners, of course, are the Lost Legends that have been added to these packs
The total cost for that ability becomes locked in, and then you can activate mana abilities to pay for it