Take an item put it into an ench. table with enough bookshelves around it put 3 lapis lazuli next to it and click the lvl 30 enchantment
If you put the enchantment table in the middle of a 5x5 outline of a square using book shelves it should give you lvl 30
Yep, should be a one block buffer between the bookshelves and the table itself, the enchantment table should not touch any of the bookshelves, if you need reference, check out "/v 7180 enchant" I added bookshelves on top for extra decoration
Not sure what you mean here, the maximum level for some enchantments vary but normally it won't go beyond V ( like Efficiency V). You need 30 XP levels, 15 surrounding bookshelves (note: you need 1 empty block around the table) and 3 lapis lazuli in order to have the option to use level 3 enchantments. Also note that it'll cost you a maximum of 3 XP levels. So don't let that fool you either, the lapis more or less compensates for that. This website explains the whole process in more detail.