At the moment scientists think that it probably does, because its the best idea we have for what could be making the universe expand in the way that it is. Some people have come up with other ideas for that though, so I don’t think that we are sure yet. Hopefully one of the others can tell you more!
Yes. Dark energy and dark matter both exist. While scientists are not able to directly see dark matter or dark energy, they can see its influence on nearby galaxies.
The Hubble space telescope, one the microscopes we have orbiting the earth, has directly observed gravitational lensing – an effect predicted by Albert Einsten many decades ago. This means that light “bends” in different ways around areas where there is large accumulation of mass (which can be either a black hole or dark matter) and we can detect this bending, directly confirming their existence.
The nature of dark energy is still very much a subject of debate and there are plenty of experiments that are currently ongoing!