Items in the game are what makes your champion as strong as they can be. The more gold you have = the better items you can get = how much stronger you become. There are a lot of items for many different roles. Items to make you more tanky, do more damage etc. So certain items are better for certain champions. These are called the Recommended Items.
Recommended Items are a basis of what the champion should have/use when playing a game to make them more powerful. Items start off as cheap things that can be upgraded into better items.
Some items have their own abilities that can be activated by through the keys 1 throw 7 and depending where they are sitting in your item slots. For starting out in League of Legends, you mainly want to follow the build path of the Recommended Items.
Later down the track you will find other peoples builds that they use or customize your own, just work out what the champion needs for his abilities to be stronger and you will be fine!
League of Learners 