The Torah (Bamidbar 31:23) commands us that utensils which were acquired from a non-Jew and made from gold, silver, copper, iron, tin, or lead, must be toiveled (immersed in a mikvah) before they may be used with food. Glass utensils must be toiveled as well, based on a rabbinic requirement. If one purchased used utensils, they must first be kashered before toiveling. However, if one borrows or rents utensils from a non-Jew, there is no mitzvah of tevilas keilim. Before immersing, the utensils must be completely clean; all labels and even residual glue from the labels must be removed. Prior to tevilah, a beracha is recited.
Most regular items can be immersed without ruining them. For certain electronic items the water should be shaken out, and one can use a blow dryer to dry the inside or it should be left to dry for three days. If the item has a digital panel and one is scared that it will get ruined, he should gift it to a non-Jew who will lift it up and take possession of it. Afterwards, he can borrow it back from the non-Jew.