Target creature gets +7/+7 and gains trample until end of turn. It must be blocked this turn if able. (A creature with trample can deal excess combat damage to the player or planeswalker it's attacking.)
If the creature attacks, the defending player must assign at least one blocker to it during the declare blockers step if that player controls any creatures that could block it. Other creatures that player controls can block other attackers or not block at all.