How to get to Paris st Lazare from Marias

It is Marais and not Marias and you have to know your metro stop for anyone to give you useful advice as there are many different lines that serve this area of Paris. Your hotel will have that information on its web site.
Here is the RATP link for mapping out metro trips; be sure to adjust the time so it is daytime in Paris when you are trying this out; if you do it from the US and it is 3 am in Paris you will get weird night bus routes.
http://www.ratp.fr/itineraires/en/ratp/recherche-avancee

Marais is still a big area. Not knowing exactly where you are and your closest Metro station.
But being an inveterate subway rider, I'd take the No 7 to Pyramides and change to the No 14 to St Lazare, or take the No 1 to Concorde and change to the No 12 to St Lazare.

Not to mention that if you are staying in the northern part of Le Marais and so are near any of Republique, Temple, or Arts et Metiers stations, you could just take Line 3 directly to Gare St. Lazare. And let's not even talk about the options if you are in the Le Marais area for hotel and apartment marketing purposes, which is a much bigger area than the historic area. So to get more precise directions, you should give a more precise location such as the nearest metro stop, name of the hotel, or a nearby intersection.

As well as the RATP interactive site, you can use Google Maps. Enter your hotel address, then click on Directions and enter St-Lazare, clicking the icon shaped like the front of a Metro engine.

I downloaded an app called "Next Stop Paris" that will give you metro/walking directions to anywhere you need to go. Inlcuding times.

When I did the same, I was staying near Republique metro so it was easy to just take the 3 to St. Lazarre. Later, I stayed near St. Paul metro. That would have required a change. I let the app guide me.