Hi @VidhyaAk1,
The instances metric that is associated with an evar counts the number of times that evar fires. Occurrences counts all hits.
So for example, you have this visit
Hit 1: evar110 fires
Hit 2: evar110 persists
Hit 3: evar110 is expired
You would get a value of 1 for the evar110 instances metric. This is because the evar fired only once, it doesn't count the number of times the evar persists. And the value for the dimension evar110 will be whatever the value of the evar is.
For occurrences, it would give a total of 3, because there were 3 hits. The row with the value of evar110 (dimension) would be 2, because it fired once and persisted once. Then there would be a row for "unspecified" with a value of 1, because there was 1 hit where evar110 wasn't present.
In general, it's a good idea to click the filter and deselect "show unspecified" when working with evars, because often the unspecified column will have the most values (depending on what metric your're working with).