For crafting there are a few things to learn.

1. Motifs (styles): you learn these by getting motif books or chapters. Each racial style comes in a book, which can be found in backpacks, nightstands, etc. More exotic styles sometimes come in full books, and sometimes come in chapters (like bows, or swords, or chests) that only teach you how to craft one type of item in that style. The exotic ones come from various sources (some drop from world bosses, some from trials, etc). Reading a motif book or chapter lets your character craft in that style, and consumes the book/chapter.
2. Different crafting materials: items that you craft come in different tiers that allow you to craft items of different levels. You learn how to use the next tier of materials by ranking up the relevant crafting skill and then spending a skill point on the primary passive for that skill line.
3. Traits: you learn traits by researching them using an item with that trait. For example, to learn the Sharpened trait for a sword, you need to have a sword with that trait and research it. This destroys the item. The more traits you know on a particular type of item, the longer each new trait takes to research. The big benefit to learning traits (aside from being able to craft items with that trait) is that there are special crafting stations across Tamriel that allow you to craft sets that give you bonuses. These crafting stations work based on the number of traits that you know for any given item. So one crafting station may require you to know 2 traits on each item you want to craft as part of that set, while another may require you to know all 9 traits on each item you want to craft as part of that set.

For dungeons you can either manually form a group with other players and go into the group dungeon (in which case it will scale to the level of the leader of your group), or you can use the group finder tool. You access it from the group screen, and queue for a specific dungeon, or for a random dungeon. You need to select your role - DPS, tank, or healer. The tool then matches you with other players based on getting a party composition of 2 DPS, 1 tank, and 1 healer. Groups formed with the tool will always get put in a dungeon scaled to CP160. If you are lower level you will be scaled up to the equivalent of CP160. Or possibly CP150? I don't remember which.

Here are a couple of guides that may help you with these questions. These ones go over the basics, and more detailed guides are available on the same channel.
https://youtu.be/1nqvR-u3QnA
https://youtu.be/04Id1NALfqw