Questing is a waiting strategy. The tick climbs vegetation, grips with its back legs and extends the forelegs, which carry Haller's organ, a sensory pit that detects carbon dioxide, ammonia, heat, humidity and vibration. When a host brushes the extended legs, the tick grabs on and crawls, usually upward, to find a feeding site.
This is why dog ticks are found along grassy trail edges and field margins rather than deep in closed canopy. It is also why they are commonly picked up on the lower legs and then found later at the waistband or hairline: they climbed there after boarding. The tick has no wings, no jumping mechanism and no habit of ambushing from height.
Questing is expensive. A tick loses water while exposed and must periodically descend into leaf litter to rehydrate by absorbing water vapour, which it can do using hygroscopic secretions from its mouthparts. How long an individual can quest before that becomes limiting depends heavily on humidity and is not fixed.