Walk around your building with your cellphone, or whatever device picks up the signal you want to access. Identify which side of the building has the strongest signal, because that's the side on which to mount the antenna.
Named for its inventors, the Yagi-Uda antenna -- often known simply as a Yagi -- is a Japanese-developed radio aerial. Rather than sending or picking up signals on all sides, Yagis are directional antennae that receive and send signals from a specific direction. Because Yagi's focus is only one direction, it doesn't lose as much power over a long distance as an omnidirectional aerial. If you make a phone call from a remote location, the signal is stronger with a Yagi. Yagi antenna also provide television or wireless Internet in remote locales.
Locate the best place on the good side of the building to mount the antenna. A vertical or horizontal pipe, roof edge, wall, window sill, balcony or fence post are all possibilities. The higher you elevate the Yagi, the stronger a signal it can receive, but if the cable from the antenna is too long, the signal loses power as it travels the wire.
Mount the antenna and connect it to the relevant device, such as your cellphone or your laptop's external antenna port. You may have to use an adapter to make the connection, but until you have the Yagi and the device hooked up, you can't tell if it's receiving the signal.
Check the signal, rotate the antenna 10 degrees and check again. Complete a circle, mapping out the strength of the signal as you go. Use the map to identify the strongest signal, point the antenna in that direction and tighten the mounting bolts.