Refracting Telescope
A refracting telescope uses two lenses to minimise the image and send it to the eye. The lenses must be separated by the sum of the focal lengths of the lenses.
Reflecting Telescope
A reflecting telescope uses a curved mirror to focus the light and a lens to minimse the image. Its advantage is that it can be much smaller than a refracting telescope but the disadvantage is that you lose some of the image because of the space taken up by the secondary mirror.