If you're a beginner, how would you know how to build a champion properly? As a beginner, the general thing to do (other than going PVP first thing and having your teammates rage because you fed so much) is to practice on Bots. Naturally, you should use easy-to-use and easy-to-know items on the Champs you use until you become proficient enough that you can tell what the Champion is capable of; then, it's off to get different, harder-to-use items. After you're proficient enough not to feed your lane, go into PVP and test yourself. If you still end up feeding, go back to bots again and practice more until you're sure you can do well enough. If not, and you end up doing well, play more PVP and find your own way of doing things against other players.
If you become capable or self-assured enough you can build bork on Jax without doing badly with him, go right ahead and do so. Beginners are in that stage that they need to get used to thinking "hey, this item has an Active ability, I need to get used to it if I want to become really good at this item!" You should use BT and tank items until you get used enough to using the character and items that you can expand away from that.
Even apart from all that, League of Legends is all about having fun. So you don't use a good build, oh well. You have fun, you learn what to and what not to do, okie dokie you're set to have a fun match. Most people don't start with a professional's mindset, and those that do start that way are more likely to uninstall because they feed and get angry about it. When you become a professional, you learn that playing certain builds can cost you your game and therefore the fun that you and your teammates could have...so you play the builds that win you games, or use the items you're most proficient with. It's common sense, mate.