Lots of different ways. If the magic item is a piece of equipment like a sword or a piece of armor, you can create it as a piece of equipment and put in the modifiers. Use existing items from the compendium as a guide. Personally, I use handouts. They detail the magic items and keep track of what players have. You can make the handouts visible to players when they get the item and file them into folders dedicated to those characters once they are divvied up. This also allows you to have an image associated with the item, plus a name, lore and quirks to really customize them. For consumables like potions, I use cards. Players can look at their cards to see what potions they have, and when they use it, they play the card. Makes inventory control simple.
