I can’t find my variable in the drop-down menu.


This is likely a level of measurement or number of levels issue.  For example, a scale variable for a t-test is coded as ordinal, or you need a nominal variable with two levels and it has three (Male, Men, Female).  For either issue, go to Management tab, then click the down-carrot under the variable name, then click select either the correct level of measurement needed or Manage.  In Manage, ensure the levels are accurate by Merging or Deleting unnecessary levels.