That's a very, very vague question. The biggest repository of all things boardgames online is boardgamegeek.com, there are forums about just about everything on boardgames, and a dedicated boardgame design forum, and many subforums.
http://www.boardgamizer.com/mechanics this site explains different game mechanics. It also has a randomizer which randomises a theme, mechanic and type of victory
Comments
That's a very, very vague question. The biggest repository of all things boardgames online is boardgamegeek.com, there are forums about just about everything on boardgames, and a dedicated boardgame design forum, and many subforums.
https://boardgamegeek.com/forum/974616/boardgamegeek/board-game-design
Guess start there :) Without knowing what you're actually looking for that's the best I can help with.
http://boardgaming.com/mechanics This site have examples of board games with the type of mechanics they have