Good question though Tsalach. Truthfully i can offer some vague advice to help you get slightly further. Try adventuring, and try to farm large scale. That way you have so much supply of food you never need food again. At this point you can focus on a new goal such as finding a village that has carrots or killing zombies until they drop one (rare). I would love to tell you to farm animals is pretty simple although it still requires farming plants first. Building a pen to store the animals and then baiting them to the pen or dragging them using leads. Cows and sheeps eat and breed off of wheat. Chickens eat and breed from seeds. Pigs and rabbits eat and breed from carrots. Wolves eat and breed from meat. Cats eat and breed from fish.

=) To continue on villagers eat and breed off of nearly anything which produces iron golems. Its complicated to make a Villager breeding camp. So I'll let you google / youtube that one. Diamond,Gold, Redstone, and lapiz are all found from level 1 - 15 high while digging as deep as you can. Many players believe digging at lvl 12 to 15 is effeciant as usually this is just high enough to walk over lava pits. Obsidian is made from mixing lava and water, in that order. If you do water then lava you will make stone or cobble.

Certain materials can not and will not be found unless you explore on a large scale. Whether it be going to the nether sailing around an ocean for hours, even finding a nether base, going through abandoned mines, or making an ender portal. Worse case scenerio you end up exploring for hours across the world.

My only advice to getting further on your lvls from 18 - 32 isnt very bad. Although you should focus on living through fights not fall off ledges. One last thing to know is if your too scared or bad at combat literally... Start cooking alot so that you may keep earning exp. Otherwise set up farms that will give exp. Even breeding gives xp.