Someone can tell me where can I find infos about how to translate IL?

i.e. how to read something like this?
Code:
  IL_0040:  ldc.i4.1
  IL_0041:  add
  IL_0042:  stloc.s    V_4
  IL_0044:  ldloc.s    V_4
  IL_0046:  ldc.i4.s   40
  IL_0048:  blt.s      IL_002a
It would be nice also to know how to translate a .net exe into IL as the ildasm.exe do.

Some help?

Thanks!