The ability to render a wall properly is a skilled trade, this isn’t something we’d recommend getting an amateur to do. The rendering material is applied to the masonry with a trowel before being smoothed out to create a beautiful finish.
Refer to this video for an introduction to the technique.
Some modern chemical renders have been designed to be sprayed directly onto the wall, although these are generally thinner and require several coats to build up.
You don’t have to render an entire house to change its appearance. A new trend emerging in home design is to only render certain portions of the exterior for aesthetic purposes.