Can you ID this hose?

[cra2]

Newbie here,

The check engine light came on in my stock 2003 Explorer 2WD, 2-door, 4.0.
I peeked under the hood (for the first time) and saw a hole in the elbow tube pictured in the links below.

a) what is it?
b) how critical is the hole?
c) are there instructions anywhere for replacing it myself?

Here's a wide shot of the area where it's located (for orientation):

Here's a closer shot, showing the small puncture in the lower of two tubes:

Here's a closeup of the part - a soft rubber "elbow" that seems to make a vacuum sound when the car's on:

As you can see in the close-up, the hose was bitten by a two-fanged venezuelan vampire hose-biter bat!

And, as you can see in the wide shot, I just put some tape on the large (also unidentified) hose on the left because I saw that it is rubbing against the corner of the handle for the transmission fluid. It has rubbed through the sheath around the tube and begun wearing a hole in the tube itself. (again, don't know how critical that is, but I thought I'd at least slow it down until I found out. hence the tape)

thanks for any input!
cra2

 

[99SportX]

It looks like a vacuum hose or PCV hose.

A vacuum leak allows unmetered air to enter the intake manifold and will cause the truck to run lean. The O2 sensors may have detected this leak via reading a lean mixture and turned on the CEL.