Nani mo （なにも）and Nan demo なん でも

なにも (NANIMO) is only used in a negative sentence and なんでも (NANDEMO) is used in a positive sentence.

Let me give you some example sentences.

Using なにも (nothing/anything)
1) きょうは なにも たべませんでした。(KYOU WA NANIMO TABEMASEN DESHITA) = I didn't eat anything today.

2) れいぞうこに　なにも　ありません。(REIZOUKO NI NANIMO ARIMASEN) = There is nothing in the refrigerator.

3) なにも いりません。(NANIMO IRIMASEN) = I don't need anything.

Using なんでも (anything/everything)
1) わたしは　なんでも　たべます。(WATASHI WA NANDEMO TABEMASU) = I eat anything/everything.

2) れいぞうこに　なんでも　ありますよ。(REIZOUKO NI NANDEMO ARIMASUYO) = I have everything/many things in the refrigetator.

3) プレゼントは　なんでも　いいです。(PUREZENTO WA NANDEMO II DESU) = As for presents, anything is good for me.

When it comes to いつも (ITSUMO/always) and いつでも (ITSUDEMO/anytime), they are both used in a positive sentence.  It may be easier to understand the difference between these two words since the English meaning don't change depending on the context.

Using いつも (always)
１）わたしは　いつも　うちで　ばんごはんを　たべます。(WATASHI WA ITSUMO UCHI DE BANGOHAN O TABEMASU) = I always eat dinner at home.

2) たなかさんは　いつも　でんわしています。(TANAKA SAN WA ITSUMO DENWASHITEIMASU) = Mr. Tanaka is always talking on a phone.

Using いつでも (anytime)

１）いつでも　うちに　きてください。(ITSUDEMO UCHI NI KITEKUDASAI) = Please come to my house anytime.

2) わたしは　いつでも　どこでも　ねられます。(WATASHI WA ITSUDEMO DOKODEMO NERAREMASU) = I can sleep anytime anywhere.