To add inventory to a product:
CATALOG > MANAGE PRODUCTS
Choose the product
Select ERP View on the top right
Look for the section labeled “New Stock Movement"
Select a “To Warehouse” - default
Add a quantity
Add a brief description - (ex. new inventory)
You should see a log show on the bottom of that screen of the added stock.
There will be a button labeled “Force Stock Updates" in the upper right-hand corner. Click that to ensure stock levels have been updated for the frontend.
If you still do not see a change one the frontend of your website you'll need to reindex the site.
SYSTEM > INDEX MANAGEMENT
Checkmark "Category Products" and "Stock Status" and hit submit.