There are many ways to do this, but the best solution for you will depend on what kind of equipment you use to shoot, where you will be shooting, and what kind of software you use to process your shots.
There are some inexpensive GPS devices (under $100 US) that do nothing but record GPS tracks. After you're done shooting, you use a software tool that comes with the device to geotag your shots, or you can convert the GPS track log to something Lightroom understands, and let Lightroom do it. It's important to make sure you set your camera clock as precisely as you can, because the geotagging software relies on shot time to link to the coordinates of where the GPS device was at that same time.
I have one of those inexpensive GPS devices, called an "iMOD" I believe, but I don't use it very much now. Instead, I use an even less expensive iPhone app to record the GPS tracks, and then geotag the photos with Lightroom. The only disadvantage to that process is that some kinds of phones cannot record a GPS track unless they are actively connected to a cell phone network. I've never had a problem like that with my iPhones, even in the Rocky mountains.
And recently, I bought a Canon 6D with GPS built in, which solves the problem forever.