Open up your inventory, double click on the salvage kit and the icon will change to a hammer icon (IIRC), mouse over the item you want to salvage and click on it. If the item you want to salvage is in another pouch/bag, mouse over the pouch/bag with the hammer icon and a second later, it will take you to the contents of that pouch/bag.
No problem...keep in mind not all items are salvageable...red text will pop up on the screen letting you know that, and if you want to know what exactly was salvaged from your item, there will be a message in the text part of the screen telling you exactly what you salvaged.