Pick your version first
The way /give writes an item has changed twice. Before 1.20.5 an item carried NBT in curly brackets, diamond_sword{Enchantments:[{id:"minecraft:sharpness",lvl:5s}]}. In 1.20.5 that became item components in square brackets, diamond_sword[enchantments={levels:{sharpness:5}}], with names and lore still written as JSON inside a string. From 1.21.5 names and lore are written directly as SNBT, custom_name={text:"Excalibur",color:"red"}, enchantments drop the levels wrapper, and hiding parts of the tooltip moved to one tooltip_display component. Smaller changes sit in between, such as attribute ids losing their generic. prefix in 1.21.2 and custom model data becoming a list of numbers in 1.21.4, so the version list is split wherever the output changes. A command written for the wrong version usually fails with an error about an unknown component or a malformed tag. Checked against Java Edition 26.3.
Names, lore and colours
Pick a colour and formats for the name and the lore, or type & codes into the text for more than one colour on a line: &a for green, &l for bold, &#FF8800 for a hex colour. The game shows a renamed item in italics, so the command sets italic off unless you tick Italic, and the preview shows what the game will. Lore with no colour shows in the game's purple. Each line of the lore box becomes one line of lore.
Enchantments past the maximum
Pick an enchantment, type a level and press Add. A level above the usual maximum, like Sharpness 10, works by command and is marked in the list; the game stores levels up to 255. Commands also let any enchantment go on any item, and clashing ones such as Sharpness and Smite both apply.
Attributes, model data and the tooltip
Attribute modifiers change what the item does when held or worn: attack damage, speed, health, armor, size and more. A modifier replaces the item's own, so a sword given only extra health no longer does sword damage. Custom model data is a number a resource pack can read to show a different model. The hide options keep parts of the tooltip out of sight; before 1.20.5 that is the HideFlags number, from 1.20.5 each part has its own switch, and from 1.21.5 the tooltip_display component lists them.
Chat or command block
The chat box takes 256 characters, the slash included, so a long command needs a command block (up to 32,500 characters) or a function file. The counter under the command shows which it fits. Copy without / gives the command for a server console, which takes it with no slash. Everything is worked out in this page; nothing you type is sent anywhere.
Questions
Why does my command say "Unknown item component" or "Expected '='"?
It was written for a different version. Square brackets mean 1.20.5 or later and curly brackets mean earlier; within 1.20.5 and later, a name written as '{"text":...}' is for up to 1.21.4 and {text:...} is for 1.21.5 on. Set the version at the top to the one you play and copy again.
Does this work on Bedrock Edition?
No. Bedrock's /give takes an item, a count and a data value, plus a short list of components (can_place_on, can_destroy, item_lock and keep_on_death). It cannot give items custom names, lore or enchantments; use an anvil and the /enchant command there.
What is the highest enchantment level?
255. Above the usual maximum the effect keeps growing for most enchantments, such as Sharpness and Efficiency, but some stop helping or behave oddly. The preview writes levels up to 10 in Roman numerals and higher ones as numbers.
Why is the item name not in italics in the preview?
Because the command turns italic off. Without that the game would show your name in italics, the way it shows any renamed item. Tick Italic if you want it back.
Can I give more than 64?
Yes. /give hands out as many as you ask for, in full stacks, up to 100 stacks at once. Items that do not stack come one to a slot, and anything that does not fit is dropped at the player's feet.