The section contains a description of the initial stage of exploration of the Peruvian Jungle in Shadow of the Tomb Raider (the quest titled Rough Landing). Lara finds herself there after the plane crash and the first priority is getting back the equipment.
Retrieving the knife
Start the linear walk through the jungle. You have to reach the place, from which the flares were launched and then go through a narrow ledge over the precipice and drop from the tree. Walk over the fallen tree and slide down the hill to a new location.
You will reach a bigger part of the jungle and discover a camp (Plane Wreckage). You will be able to spend your first skill points there to unlock the first skills.
The most important task is retrieving the knife and the axe, thanks to which you can continue the exploration and reach another fragment of the plane wreckage, where Jonah is.
Reach the biggest part of the jungle, near the camp, i.e. the location with a small lake, in which part of the plane is. Approach the yellow propeller and examine it - it will fall into the water and you will need to dive. Reach the wreckage lying at the bottom (picture above). Lara will obtain the Knife. You will have to use it right away to kill an aggressive eel - just press the action button repeatedly.
Upgrading the knife and retrieving the bow
Get back to the Surface and use the knife to try and cut the rope shown above. You will learn that the knife isn't sharp enough.
You have to find any 3 Salvage crates - you can try and reach those indicated on the map or find some yourself. After getting enough materials, go back to the camp in the jungle. Go to the inventory tab and spend the resources on creating a Makeshift Knife. This will let you cut the rope.
Cutting the first rope won't do the trick - there's another one that needs cutting. In order to reach it, you have to climb the "interactive" tree and jump onto the rock ledge above. The place where you can cut the rope is shown above.
Now you can reach the place, where the cargo was dropped. The Recurve Bow is in the oblong crate shown above.
Note that you can upgrade the bow right after getting back to the camp, but that isn't required to progress with the main quest right now. It could make things easier, though.