From the top of the wall, near where you found the first-aid kit, you can get a good look at the next 3 enemies below. They're not roaming around, though, so you'll need to bring them to you.
From the cover of the rubble on top of the wall, use your bow to kill one of them with a headshot.
Then move back and hide next to the vine-covered wall. The other men will be alerted and come looking for you, hopefully one at a time.
While you wait for them, assess your arsenal since you will soon have no choice but to fight. In addition to her bow, Lara has a shotgun, handgun, and rifle. To switch weapons use the numbers 1-4 on the keyboard or the D-pad on a controller. (1/Up = bow, 2/Down = handgun, 3/Right = rifle, 4/Left = shotgun). You have limited ammunition, but you've already picked up a bit of rifle ammo.
You can craft more arrows by selecting the bow, then without aiming, hold the Fire button (Left Mouse/Left Trigger). This uses wood and feathers from inventory.
If Lara is injured in the upcoming firefight, you can heal by pressing F1 on the keyboard or holding L1/LB on the controller to bring up the Herbal Mixtures interface then press X/A to use medicine from inventory. (man-made medkits and healing herbs are grouped together under Medicine in your inventory. This mechanic is slightly different than in the last two games, and healing no longer uses cloth.)
Now, back to the action. Watch as the second man approaches...
He may glow red, since the two enemies are paying attention now, but that's OK. Just wait for the Melee icon to appear...
...then press the button to attack him.
Melt back into the vines, wait for the third man to come near...
...and Melee kill him too.