Cis/Trans Isomerism in Cycloalkenes
In simple molecules like what you've drawn above, see if the hydrogens are on the same side of the double bond or not.  If they are on the same side, then the compound is cis; if the hydrogens are on opposite sides, then the compound is trans.  In more complex cases, prioritize the four substituents on the double just as you've been doing with "R\S" nomenclature.  If the two highest priority groups are on the same side then the compound is cis, if they are on opposite sides, then the compound is trans.  The terms "cis" and "trans" are still used, but especially in the more complex cases they have been replaced with the first letters of the German words "entgegen" (E, opposite) and "zusammen" (Z, together).  So cis-2-butene could also be called Z-2-butene.