While there are many different shapes and styles of handheld infrared thermometers, and many features available, the basic function is very similar in very nearly every variation. The first step in taking a measurement, is determining the desired target.  All portable infrared laser thermometers regardless of design will have a means of "aiming" the instrument at the target.  Some versions simply are shaped in such a way that pointing at the target is the targeting method.  Others have a guide such as a laser spot, or group of laser spots that indicate the area being targeted.  The temperature measurement is taken when the "trigger" is activated.  This is usually a button located either underneath the pyrometer (gun style), or on top (television remote control style). The accuracy of the measurement depends on several factors.  See What is the distance to spot ratio?  to understand the elements governing accuracy.