Most addons will have 2 downloads, one for the behavior pack, one for the resource pack.

MCPacks are the behavior and resource packs, and the MCWorld are maps. At the bottom of the page there should be green download links, saying (.MCPac) or (.MCWorld). Addons and Resource Packs are installed exactly the same way as each other, so just follow these instructions, only replace the addons with resource packs.