Collect evidenceTo “collect evidence N” means to exile any number of cards from your graveyard with total mana value N or greater.
If a player is given the choice to collect evidence but is unable to exile cards with total mana value N or greater from their graveyard (usually because there aren’t enough cards to do so) they can’t choose to collect evidence.
A spell that has an ability that allows a player to collect evidence as an additional cost to cast it may have another ability that refers to whether evidence was collected. These abilities are linked. See rule 607, “Linked Abilities.” (CR 701.59) 6: This Vehicle becomes an artifact creature until end of turn.
Whenever this Vehicle attacks, you may
castTo cast a spell is to take it from the zone it’s in (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. A player may cast a spell if they have priority. See rule 601, “Casting Spells.”
To cast a card is to cast it as a spell. (CR 701.5) an instant or sorcery spell from among cards exiled with it. If that spell would be put into a graveyard, put it on the bottom of its owner's library instead.
CrewCrew is an activated ability of Vehicle cards. “Crew N” means “Tap any number of other untapped creatures you control with total power N or greater: This permanent becomes an artifact creature until end of turn.”
A creature “crews a Vehicle” when it’s tapped to pay the cost to activate a Vehicle’s crew ability.
A Vehicle is “crewed by” a creature if that creature was tapped to pay the cost to activate that Vehicle’s crew ability.
If an effect states that a creature “can’t crew Vehicles,” that creature can’t be tapped to pay the crew cost of a Vehicle.
Some Vehicles have abilities that trigger when they become crewed. “Whenever [this Vehicle] becomes crewed” means “Whenever a crew ability of [this Vehicle] resolves.” If that ability has an intervening “if” clause that refers to information about the creatures that crewed it, it means only creatures that were tapped to pay the cost of the crew ability that caused it to trigger. (CR 702.122) 2