A car moves so that

at time t₁ = 3s, its position p(t₁) satisfies p(t₁) = 6 yards from origin.

at time t₂ = 8s, p(t₂) = 16 yards from origin.

Average velocity between t₁ and t₂ =  = 2 yards / s

The velocity at time t₁ is the average velocity between time t₁ and t, with t very close to t₁. How close? So close that the result doesn't depend on t.

Velocity at time t₁ =