Note that, unless this has changed recently, SERIES tags (that you edit along with your series description and such) work, but EPISODE tags (the ones you add when uploading a new page) do nothing. The feature is there but hasn't actually been implemented, so no one can search for those tags using the tapas search.
Honestly I'm not sure even the series tags are all that useful, even though they technically work, because unless you've got a very specific and also very niche interest it's difficult to imagine anyone finding you specifically, because the results aren't really arranged in any particular way. Like, if you do a search for "necromancer" then the comics with "Necromancer" in the title will be listed before the ones that only have it in a series tag, but that's the only organisational feature I can determine.
At one point I did a search for a tag my comic had and tried to figure it out -- is it based on most recently created? Most recent update? Most subscribers? None of those seemed to explain which comics were listed before mine and which were listed after. Your spot in the list seems arbitrary, which makes it sort of difficult to work with for becoming more discoverable.
In any case, I still put a bunch of series tags on my comic just in case someone DOES search for them, and for a while I was putting episode tags on in case the feature is implemented some day, but it'd be hard to do much more than that with it.