Various scenarios can occur: gluing unfired pieces, gluing fired pieces, gluing pieces together or with other elements of different materials.
There are translucent liquid clays on the market that work as a glue for both raw and fired pieces. To have adherence they must be cooked. There is no problem refiring an already cured piece when adding adhered details such as decorations and any beads or beads that will withstand firing under polymer clay conditions.
You can then use other glues to join pieces together like high tack super glues that work right out of the box. This is traditional for positioning earring posts, prior to sealing with resin. A quick glue allows you to affirm the piece that you then cover with resin for a more professional finish.