Difference between desu and da, dewa arimasen and jyanai

[damkay]

Ok guys i have learned all hiragana and katakana, for now im learning numbers, time and some vocabulary but i have a problem because i have found two different resources that confuse me, because one of them tells me to use present state of being with DESU, negative with DEWA ARIMASEN, past with: DESHITA, and past negative with: DEWA ARIMASEN DESHITA, BUT the other resource: says PRESENT WITH DA, negative with Jyanai and so on....... IF I WANT TO SAY: it's a cat, just for nouns for now, which one do i use ?????????

[NileCat]

formal/proper/polite/decent　vs.　casual/blunt/rough
それはネコです　← works in any situation
それはネコだ　←　casual/blunt/rough/candid/frank
I personally recommend you to get familiar with the former.

[damkay]

OOooook that explains A LOT, thxs, or Domo arigatou gozaimasu (formal way always better)