you probably hit f1, that makes your hotbar disappear
Chat with our AI personalities
The bar at the bottom of your screen during gameplay also known as the "Hotbar".
It should automatically be there.
Because you have a really bad computer and minecraft is using all of the memory.
the 1 - 9 keys
The green bar under your health and your hunger is the experience bar. If you craft an enchantment table, you can pay experience to enchant tools and weapons.