Hi, this Managing Inventory using a Transactions Ledger is place to start understanding what will be needed in you solution. It was very helpful in getting me started in understand how build a solution for things like items that will go in and out of your database/solution. See what you can take away from it, and then post more questions related to to what you want to do. The post's creator and other members will likely comment on your question you have.
The simplest way to get a Value List using entered values is the option: "Using values from field"; then choose the Table (actually its Table Occurrence name, which is on the Relationship Graph). Next, keep the default option below, (•) Include all values.
Attach the VL to the field on the layout. You can then either chose an existing value in the list, or just click the field, and type a new value. It is very important to choose an existing value, if possible, to keep clear of "different name for the same darn item" (which makes many things not work as well as they should). Value List automatically shows a unique list.