What does stars twinkling have to do with the hubble telescope?

Ground-based telescopes suffer from being under the Earth's atmosphere.

Movement and different densities in the earth's atmosphere causes the light from distant stars to be randomly refracted, and this appears to ground-based observers as 'twinkling' of the stars. For telescopes, these effects cause images to be distorted and blurred, and prevent the telescope's optics from operating at their best, and from getting the best possible images of planet, nebulae and galaxies.

Although it is possible to compensate for the effects of the atmosphere with adaptive optics (literally adjusting the shape of the mirror to correct for these effects), the best way to avoid the effects of the atmosphere is not to have it there at all.

The Hubble telescope was put into orbit around the Earth so that it is permanently situated above the atmosphere, and its users never have to worry about it distorting their images - this has allowed astronomers to get the best images of, for example, the most distant galaxies ever produced.