Unless you're planning on making only tapers and pillar candles (and in this last case, if the molds you own all have a wick hole), there is no doubt you will have to use wick sustainer tabs (wick tabs, for short) to keep your wicks in place.
For every other type of candle you make, a wick tab is required, either to secure the wick to the bottom of your containers or to bring together wick and candle. A basic but indispensable widget, wick tabs come in different sizes and styles.
A tiny round piece of thin metal with a hole punched into it to form a little neck, that's about all you can say to describe the modest wick tab. But what a headache when you don't have any left!
You will use them mainly to permanently secure your wicks at the bottom of a container, using either glue wax, a glue dos or your glue gun. Press it down using a wicking needle or better, like I do it myself, with a small section of brass tube through which you thread the wick: this will allow you to apply uniform pressure on all sides of the wick tab and will prevent the wick from standing askew.
If you make votive or tealight candles using wick pins in the first case or a rubber mold in the second, the wick tab allows you to attach the wick to the candle. To make sure they both stick together like they should and don't separate, a light blow with your heatgun will melt just enough wax to "glue" the wick tab in place for good.
There's not exactly a thousand and one different types of wick tabs to choose from. Generally, they come in two or three different sizes (.6" and .8" are the most common diameters) and with a short or long neck. To wick container candles, regardless of the wax used (paraffin, vegetable wax or candle Gel), always use a wick tab with a long neck (.25" or longer if you can): when the flame reaches the neck of the wick tab, it will go out by itself, greatly reducing the risks of seeing the candle burst into flames due to the little amount of wax left. It's even more crucial when you work with candle Gel; candle Gel burns hotter than any other wax (the temperature inside the melt pool can easily get as high as 280°F whereas paraffin only reaches 180°F) and this increases the potential for a fire hazard. Short neck wick tabs, usually about .12", should be reserved for pillar and tealight candles.
To secure the wick tab to the wick, once you've threaded the wick through the wick hole, all you have to do is gently squeeze the neck of the wick tab with long nose pliers. Make sure the wick has been primed first, it's not only necessary to ensure an optimal combustion, it also makes it much easier to thread the wick through the wick tab.
Due to their flat shape and their width, wooden wicks need to be clipped into a special type of sustainer tab. Remember to order them together with the wicks or you could end up paying more for shipping than for the actual sustainer tabs...