• Global symbol requires explicit package name (en) also explained in Variable declaration in Perl (en)
• Use of uninitialized value (en)
• Bareword not allowed while "strict subs" in use (en)
• Name "main::x" used only once: possible typo at ... (en)
• Unknown warnings category (en)
• Can't use string ("Foo") as a HASH ref while "strict refs" in use at ... explained in Symbolic references in Perl (en)
• Can't locate ... in @INC (en)
• Scalar found where operator expected (en)
• "my" variable masks earlier declaration in same scope (en)
• Can't call method ... on unblessed reference (en)
• Argument ... isn't numeric in numeric ... (en)
• Can't locate object method "..." via package "1" (perhaps you forgot to load "1"?) (en)
• Odd number of elements in hash assignment (en)
• Possible attempt to separate words with commas (en)
• Undefined subroutine ... called (en)

perldiag contiene explicaciones más extensas sobre cada uno de los errores y warnings, puedes ojear esta página o puedes acceder a una explicación especifica como se muestra en usando diagnostics o splain (en).