Let's cover some of the cases. Adjectives The hyphen is required in adjectives which: 1. Denote the shade or combination of colors: светло-розовый, красно-желтый. 2. Derived from the compound nouns: бета-активный. 3. Сonsist of equal parts: Русско-Английский. 4. With use of the prefix "half": пол-лемона. Prepositions The hyphen is written if the following prepositions are used: из-под, из-за, по-за,по-над. Particles These particles are integrated in the text with the hyphen as well: -нибудь, -то, -тка, -либо, кое-. Numerals Remember that the numerals are written with the hyphen when there is a number in front of the word: 7-тысячный, 5-сотый. I hope this helps:)