The following chapter will feature useful information on taming mounts, enabling you to use them as a means of travel.
In addition to standard fast travel, Horizon Zero Dawn also enables Aloy to hack and take over some of the machines (striders, broadheads, and chargers, making exploration that much more effective. The option to tame a mount becomes available only after a certain point in the plotline, but it's not that far into the game to become a bother.
How to tame a machine?
The first, and essential, step is to approach the machine without being detected. Each of the machines will react differently to your presence, but all of them are hostile by default. If the machine notices you, it will warn other nearby machines, and they will either escape or begin attacking you.
If you want to use a machine as a mount, you can neither attack it, nor set any traps - it is essential that you don't. Remember also that once tamed, your machine may be attacked by other members of its species.
To override a machine, you'll have to approach it unnoticed, and then press the appropriate controller button (triangle by default) and hold it until the date transfer is complete. If you stop half way, the machine will not move, only stand as if it were stunned; you can complete the procedure at your leisure.
Once the process is complete, the machine's lights will change color to blue. From now on, you'll be able to ride it, assuming you've tamed a strider or broadneck. Other creatures will simply become your allies and support you in combat if you're attacked. You'll learn the ways to hack some of the mounts after completing cauldrons and extracting the information they contain.
Perks of having a mount
Having tamed a machine, you can use it to significantly reduce travel times during long-distance trips. What's more, if you order your mount to stick to the roads (there's an option in the game settings), you can even fight while sitting on its back; now the only decision left fro you to make is which direction to take on road intersections.
Furthermore, when dismounted the machine will support you in combat, providing additional fighting force in dire situations. If you choose to remain on top of your mount though, you can attack your enemies with the attacks delivered by your mount. You control them yourself using the controller, but learning to use them effectively takes some time.
If you leave your mount behind, you can call it by whistling. The relevant icon is marked on the picture above. The effective range of the whistle is rather wide, but don't expect your machine to rejoin you after being left on the other side of map.