Mario wrote:

> I'm trying to learn a little latin for my conlang but I haven't been
> able to find sufficient explanation of what declension is for.  I have
> seen it in a few conlangs but still don't understand it. If anyone could
> explain it in simple terms for me that would be great.:)
Declensions are just the patterns of how nouns changes for case.  It is
analogous to the conjugation of verbs.

When (and if) you decide to have cases in your conlang, you need some sort
of pattern for how the nouns decline. Some langauges have rather clear
Basque (where all nouns (I believe) add the same suffixes without any
changes to the stem or the suffix):
Absolutive: gizon 'man'
Ergative: gizon-ak
Dative: gizon-ari
Genitive: gizon-ako
Comitative: gizon-arekin
Inessive: gizon-an
Aditive: gizon-ara
Ablative: gizon-atik

Most languages, thought, add complexities.  Turkish for example has a lot of
phonological constraints:
bas (with a tail on the s) 'head'     ev 'house'
Nom. bas                              ev
Acc. bas-I                            ev-i
Gen. bas-In                           ev-in
Dat. bas-a                            ev-e
Loc. bas-ta                           ev-de
Abl. bas-tan                          ev-den
(I=undotted i)
The complexities here, though, are still transparent.  Turkish has what's
known as vowel harmony--thus the first word with its back vowel in its stem
has all suffixes with back vowels, the second word with its front vowel in
its stem has all suffixes with front vowels.  And the t/d alternation in the
locative and ablative is explained because the t will appear after a
voiceless sound (like s with a tail) and the d will appear after a voiced
sound (like v).

And finally there are declensions with complexities that aren't transparent
at all and one cannot separate the words into clear-cut morphemes (as I did
above).  Greek and Latin frequently are like that as is my lexiconless,
just-for-grammatical-fun conlang, Kuvolan (from which these examples are
        Indefinite                        Definite
        sg.                pl.            sg.        pl.
Nom.    'ediin 'weapon'    'ediinax       'ediiso    'ediinaxo
Acc.    'ediit             'ediitax       'ediiso    'ediitaxo
Rel.    'edin              'edinax        'ediiso    'edinaxo

(Orthography note: '=/?/ VV=V: x=/S/)
(Terminology note:  Nom.=nominative, Acc.=accusative, Rel=relative,
indefinite=without the definite article, Definite=with the definite

While these words were derived using specific phonological rules, in the
forms you see above, the morphemes are blurred.

Hope this helps, and I'd be happy to answer any and all questions this post