The reputation levels are like this:
150 Create a tag.
This is the bare creation of the tag, no tag wiki or guidance.
Nobody else has to approve the creation.
You create a tag simply by typing it into the tag field of a question.
1250 Create a synonym.
This proposes that two tags be made synonymous. One being the master tag and the other pointing to it.
You must not only have 1250 reputation but also an answer score of 5 in the tag.
Other users with a score of 5 on the tag may then vote on the synonym proposal. Four upvotes creates the synonym or two downvotes reject it.
A moderator's vote is binding.
1500 Approve tag wiki edits.
Anyone may suggest an edit of a tag wiki (or creation if none exists).
Users with 1500 reputation will see this suggestion appear in the Edit Review queue alongside suggested edits to posts.
4000. Trusted User.
A trusted user may perform tag wiki edits without them being reviewed by others.
If you are not seeing this behaviour, then please let us know more details of what error messages you are getting.