Scope of it
While senior ICs are good with leadership without authority and you are probably coming from this background anyway, EMs have a bunch of legitimate authority that comes with the role itself.
You have to define with your own manager what is the scope of this authority and what you can and what you cannot do by yourself. Can you fire people on the spot? Probably not, you won’t be able to pull a classic Donald Trump move in a meeting.
This is where the line is very blurry for AMs in Delivery Hero. They keep their IC title unfortunately in workday/slack and this brings confusion to the team. Anyway it’s simple as the AM you don’t have the authority to do much and everything will be cross-confirmed by your own manager. Nonetheless, if you are an AM, you should ask your manager to explain to the team what you are doing, that people should refer to you as their manager and that you are in charge.
Using authority
While using your new acquired authority can be tempting because it’s the most effective in terms of length of decision making you should avoid using it as much as you can. It’s a power-move, and you’ll have to use it, after all a company is not a democracy, but there will always be long-term repercussions on either morale, trust or more generally how people will perceive you. You should keep this super power for yourself as much as you can. You are the boss but don’t be bossy.
Worse than using authority for a decision would be using rewards for decisions: “you’ll get A if you do B”. Not only it sets expectations for future rewards (todo expand on this).
Even worse++ than the above is using threats or repercussions to get something. That will immediately backfire and shouldn’t be used at any time.
What you should be looking for is Referent Power and this is built over time as it comes from trust and being respected. It comes with a few principles: (to be filled).