Discussed a lot out here before....Do a search.
However these Checks may differ from Airline to Airline & Aircraft to Aircraft.
Just giving you an example of one Type.
These Checks are varied by Flight hrs & also calender period [to cater to less flying Aircraft].
Check A is normally a 125 hr check.[Takes a few hrs]
Check B is normally a 750 hr check.[Takes a day approx]
Check C is normally a 3000 hr check [Takes 5-6 days approx,depending on shifts]
Check D is normally a 18000 r check [Takes 2-3 months]
They differ from each other in the complexity of each check,certain extra work is involved,certain non accessable items are checked,mainly higher checks concentrate more on Structural inspections.Corrosion Insp is a major check carried out.
It can go on depending on the Hours an Aircraft flies,As an aircraft ages certain CPCP [Corrosion Prevention & Control programme],SSID [Supplemental Structural Inpection Document],Aging Aircraft checks are added.
The Design Ecnomic age of an Aircraft is normally around 20 yrs.
The problem is it getting difficult Economically to maintain.
Aircraft Items from a vendor do come with a release note,stating that the item is from an approved source.