Sigma 70-300mm F4-5.6 DG OS is an Auto Focus (AF) Telephoto Zoom lens with 35mm FF max sensor coverage. When mounted on a 35mm FF sensor camera, it will give you an FF equivalent focal range of 70 - 300mm. With a max aperture of f4 at 70mm, we can not consider this lens fast on wide end and neither at tele end with its f5.6.
This lens features on optical image stabilization which helps capturing sharper images at lower shutter speeds. Sigma 70-300mm F4-5.6 DG OS is not a weather sealed lens, so you have to be extra careful against rain and dust.