The /itemname command can be used to rename the item you're currently holding. Requires operator or the customname.itemname permission.

Similarly, the /itemlore can be used to set the lore of an item you're holding. Requires operator or the customname.itemlore permission. \n can be used to create new lines, \\ can be used to escape a backslash.

Similar to the /name commands, running these commands without arguments resets the item name/lore of the item you're holding.

Minecraft's formatting codes can be used to format your prefix, suffix, nickname, or your item names/lores. Instead of the § character, use & (to use & in an (item)name, type &&). Alongside Minecraft's default formatting codes, the &#<hex code> format can be used as well.

Useful tools to easily create formatted names are available here and here. Usage of formatting codes in names can be disabled in the config file.