My 2006 Ford ranger 4.0 is making a clicking noise when accelerating. I added a video, can someone tell me what that part is that’s cracked? Thank you.

 

Both audible & visual clues in your video: diesel-like ticking\clacking & a very visible crack in front end of left ValveCover.
Your FrontLeft TimingGuide is broken, allowing that TimingChain to slap ValveCover.
OrginalCause is FrontLeft OilPressurized TimingTensioner failed, likely due to dirt\sludge in the oil,
allowing Chain slap, causing Guide to break & cracking ValveCover.
The 2 OilPressurized TimingTensioners (FrontLeft+RearRight) should be renewed every 75k~100kMiles\10Years
& Oil+Filter should be changed every 5kMiles\6Months, or this will result.
Recommend NOT driving vehicle until fixed; catastrophic engin damage can occur if TimingChain jumps teeth.
Fixing FrontLeft TimingChain+Guide can be done with Engine in vehicle.
Fixing RearRight TimingChain+Guide requires pulling Engine.
Click here for more info on TimingTensioners+Guides+Chains for the V6~4.0L~SOHC.