Answer: one way is that the atom will share an electron. Sorry i only know 1 way
Explanation: for example, if Cl with 7 electrons wants to bond with Ar, that has a conplete set of 8 electrons, then Ar will share its electron to fill in the space of the missing electron in Cl.
*JUST AN EXAMPLE. IM NOT SAYING CL AND AR DO FORM A BOND.