A new SW tank needs to cycle before adding ANYTHING living to it. A cycle usually takes about 4 to 6 weeks. Please Google 'nitrogen cycle' for marine tanks.
You should have your own test kits (ammonia, nitrite & nitrate & PH) to watch your cycle and see the progress.
Typically after the cycle is finished you will add a clean up crew (CUC) , if all goes well with that you can add a fish.
An anenome is out of the question at this point, as there shouldn't even be fish in the tank yet. As mentioned you are looking at easily another months before your tank may be ready for an anenome, and then only if it is stable.
Buying pre-made SW is no substitute for cycling a tank unfortunately. It is basically no different than making your own SW at home using a salt mix.
Can you tell us more about the tank please?
Tank size and are you running a sump?
Lighting, equipment, skimmer, heater..etc - whatever you have.
I would suggest you purchase a really good book on SW tanks so you can learn what you need to know to set one of these up properly. I would suggest the following book:
The Contentious Aquarist by Robert Fenner