1) Speed is considered to be the distance travelled divided by the amount of time it takes to span that distance. It is in terms of how fast something is moving relative to the Earth (unless otherwise stated). Velocity is the combination of speed and motion. An example of something with a negative velocity would be an object moving in the opposite direction of what one has labelled as “positive”. For example, if I’m describing the velocity of a bike moving at 12 mph due East, East would be considered my positive velocity. If the bike were moving 12 mph due West instead, the velocity of said bike would be considered negative.
2) Velocity is how fast something is moving and the direction it’s moving. Acceleration is the rate of change of velocity, with respect to time (measured in seconds usually): whether it’s increasing or decreasing.