We are having an increasing number of tags being created, many are a simple case of being synonyms.
How can we create tag synonyms in these early stages?
I don't believe we can yet.
Users with more than 1250 reputation and a total answer score of 5 or more on the tag, can suggest tag synonyms.
Until we get users with that amount of reputation (which probably won't take too long), we'll have to wait until pro tem moderators are appointed.
The Stack Exchange community team keeps a close eye on newly launched sites to make sure everything goes smoothly. They usually take care of the moderating duties until we have pro tems.
If you think a synonym is appropriate, make a post about it on meta. If there is a community consensus, you could try flagging the post for moderator attention. Someone on the comms team would see it and handle the flag.
For cases where we want a synonym, as JohnB said the best bet is to make a tag-specific post. (I've seen that on other sites even when there are mods -- the community should be involved in making the decision, after all.)
But not all currently-redundant tags should be synonyms. The questions tagged cat were tagged before cats existed; had the latter existed, somebody typing "cat" would have been offered cats. There is no reason to create a synonym there; this is a matter of (a) early tags that we should just clean up and (b) teaching users new to SE to pay attention to the auto-complete offerings. I don't think there's ever a reason to have a synonym that is a proper subset of its associated tag; synonyms are to catch cases of different vocabulary (e.g. if we decided that "discipline" and "training" should be synonyms -- I'm just making that example up, not proposing it).
Tags that were created and have no questions will age away on their own, but it takes months. In these early stages we may want to request burnination of cat and any other common mis-tags just to prevent accidental selection.