The chapter below contains a complete walkthrough for The Point of the Spear, including screenshots and boldfaced tips.
This quest is the first one that can be taken at will. Begin with saving the game - you can also choose to skip the mission for a while and embark on a short trek to gather some plants and useful items.
Hunting Striders is rather easy, provided you stay calm. Keep looking for weak spots - a well-aimed projectile will confuse the machines. Don't forget about Watchers - eliminate them first so they won't alert the rest of the herd.
Once you've gathered enough material, craft fire arrows. You can use the dedicated tab in the extended interface. In all, you'll need to prepare 20 fire arrows.
Use the opportunity and visit the vendor to buy a Tripcaster. It's a very useful weapon that enables Aloy to lay tripwires, used to immobilize some of the machines.
The trader can be found near the settlement, in a small house that can be seen on the screenshot. Talk to him and buy the weapon. Take a look at other wares, especially the free samples that are offered by every trader.
If you've managed to complete both objectives, return to Rost. You can find him sitting on a tree trunk right next to a campfire. Talk to him first, then interact with the said campfire to proceed forward.
The duo will embark outside of the Embrace. Follow the trail of wrecks and search through all destroyed machines. Your final objective will be to defeat a Sawtooth. To get some tips on how to defeat him, visit the dedicated chapter of this guide. Eliminate the machine and take its heart. If your inventory is full, either delete or craft some less demanding items to free up the space.
The quest will end with a short cut-scene and a dialogue. You'll receive a new task - Mother's Heart.