Picking up items/Inventory

how to i code and save the users inventory?

Try the search engine in the forum. This topic is a very popular one, and you will find several examples and ideas on what kind of inventory best fits your game style. In short, creating an inventory Item class, and holding these items in an array, is a good way to go. Then the array can be saved with player.Prefs. A special array class of player.Prefs found in the wiki.

thanks!