All summoners need pouches to summon their familiars. Through the power of the obelisks, they are able to bind the essence of a creature into the pouch to be released later. In addition, they can use these pouches to create scrolls to empower their creatures to use special abilities.
To infuse any pouch, you need an empty pouch and a few ingredients. By taking these to a fully-charged Summoning obelisk, you will be able to infuse the pouch so that you can summon your familiar. To find out where a suitable obelisk is, read summoning locations.
When you find an obelisk, you can simply click on it to bring up the options for infusing a pouch. Depending on the ingredients you have to hand, it should look something like this:
You can remind yourself of the ingredients you need by selecting a pouch in the interface. Like many other skills, you have options for infusing many pouches at once.